Traveling from Pontianak, the capital of West Kalimantan province in Indonesia to Kuching, Sarawak, Malaysia, or vice-versa, in a day can be easily done by flying, driving, or by catching buses. Of course, the level of comfort, and how much you end up spending, will depend on what mode you choose.
Getting from Pontianak to Kuching, the capital of Sarawak, can be seen as one leg of the "Extended Borneo Overland Trail" which can be covered continuously between Tawau at the southeastern tip of Sabah, and Pontianak at the western end of Borneo. Sabah and Sarawak are both part of Malaysian Borneo, while West Kalimantan is an Indonesian province but the trail also require you to pass through the expansive sultanate of Brunei which lies more or less in between the two states of Malaysia.
The stretch covered by this leg can be both challenging and fascinating; challenging because it involves travelling through some of the more remote corners of West Kalimantan and Sarawak where the roads may not be at their best. The trip can also be fascinating because you will get to see the contrasting differences between the Indonesian and Malaysian side of Borneo.
This itinerary basically just shows you the way to get from Pontianak to Kuching and does not leave you much time for any diversions.
There isn't really that much to prepare for as the route goes through many small towns where you will be able to get food and drinks -- and accommodation if you get stranded -- without any problems, although the accommodation in the Indonesian side (except in Pontianak where 3-4 stars hotels and international chain restaurants such as Pizza Hut and KFC are available) of the travel tends to be very basic. If you are driving, just make sure that your car is in good condition as there are many stretches where you'll have to wait for a while before you can thumb a lift to the nearest mechanic.
As the route brings you across state and international borders, make sure you satisfy the necessary immigration requirements.
The fastest and most comfortable, but also the most expensive is through Batavia Airlines  which operates four flights weekly and Kalstar Aviation which operates daily flight between Pontianak and Kuching. The flight takes about 40 minutes. There is also talk about Air Asia and MAS Wings potentially servicing this route.
Even with your own car, the journey from Pontianak to Kuching by road is taxing, taking anything between eight and ten hours. The road condition is partly sealed, with much of the roads in extremely poor condition requiring you to slow down to a crawl or complete stop to navigate potholes.
The journey is described in stages from Pontianak to Kuching. If you are traveling the other direction, just take the stages in reverse:
Pontianak to Sei. (Sungai) Pinyuh (50km): The drive out of Pontianak is quite straight forward. Road conditions are fair and the road heading north from the city is a two-lane road, passing the busy coastal town of Jungkat.
Sei. (Sungai) Pinyuh to Ngabang (127km): At Sei. Pinyuh, the road is split in two directions with a round-about in the middle of town. Turning left will lead to the north shore towns of Mempawah, Singkawang, Pemangkat, Sambas and Bengkayang. (Border checkpoints with Sarawak in Sambas and Bengkayang are planned by Indonesian government.) Turning right will lead to the hinterland (and Sarawak) towns of Ngabang, Sosok, Tayan, Sanggau, Sekadau, Nanga Pinoh, Sintang and Putussibau. The road from Sei. Pinyuh to Ngabang is a two-lane road, and drivers are cautioned to drive carefully as parts of the roads are damaged by heavy traffic and poor maintenance by the local authority.
Ngabang to Sosok (38km):Ngabang is a major stopping point for food and accommodation before the border checkpoint.
Sosok to Balai Karangan (80km):Sosok has the potential to become an important transit town in West Kalimantan as it lies in the intersections of roads leading to border checkpoints to the north, Sanggau, Sekadau, Nanga Pinoh, Sintang and Putussibau to the east, Sei. Pinyuh, Pontianak, Singkawang to the west, Tayan to the south (Roads linking Tayan to Pontianak is currently under-construction, and once completed it will cut short the travel distance between Pontianak and Sosok by at least 2 hours. Another road is being scheduled linking Tayan to Sandai and Ketapang in the southern hinterland and south coast of West Kalimantan).
Balai Karangan to Entikong Border Checkpoint (19km):Balai Karangan is the last town in the Indonesian side before the checkpoint. The Indonesian side of the border checkpoint is called Entikong, while the Malaysian side is called Tebedu.
Entikong and Tebedu Checkpoints: Once in the Entikong checkpoint area, there are two clearances needed. The travelers are required to get out of their vehicle and clear immigration by lining up for immigration stamps. After clearing the immigration, passengers can return to the vehicle while drivers are required to report vehicles exiting the country to the local police station at the border. Once paperwork is done, the vehicle can be driven out of the country towards Sarawak's border which is a mere 50 meters away. Once in the Tebedu checkpoint area, all travelers are again required to get out of their vehicles and line up for immigration stamps. Drivers will again require to report vehicles entering Malaysia and pay for a one-month vehicle entry permit. Customs will then check for baggage and vehicles. Please note that foreign vehicles are prohibited to have tinted windows when entering Malaysia.
Tebedu Checkpoints to Serian (50km): From the Tebedu checkpoints to Serian is about 40 minutes of mixed roads between two-lane roads and dual-carriage ways. Serian is a transit town for most Indonesians who wish to come to Kuching and vice versa.
Serian to Kuching (56km): From Serian to Kuching is about 30 minutes of 56km-long dual-carriage ways. It is a good paved road (which can be considered as a highway). Before reaching Kuching, there are several suburban towns along the way, such as Tarat, Tapah and Siburan. After Mile 15, the dual-lane roads will shrink at a signalized intersection (near Sedap Food Industries factory). On the left is a road leading to Mambong, while on the right is a road leading to Kota Samarahan. The road to Kuching is just straight ahead. The road is undeniably busy as it is a bottleneck between two highways. The split to the dual carriageway begins again at Padawan town (just around 10km from the Mambong junction). Then you will pass several satellite towns, such as Penrissen, Kota Sentosa (locally known as Pasar Batu 7), Batu 4 and Batu 3. After going through a busy road at Kota Sentosa, there will be two junctions to Kuching International Airport. Straight ahead is a road leading to Kuching.
For your information, Kuching city lacks vital signboards, especially the one leading to Petra Jaya, Santubong, and other suburban areas. Always have your maps handy to avoid being lost in the city as Kuching is a considerably large city.
There are plenty of bus companies between Pontianak and Kuching. The cost of a return economy class ticket is about IDR380,000 (USD38, 40-50 seats per bus), IDR 200,000 for one-way (At some places it is also possible to pay in MYR since most of the companies are malaysian). While a more comfortable Super Executive class is IDR300,000 (USD32) for return trip (larger size 20-25 seats per bus). As of September 12th, buses will depart and arrive at Sungai Ambawang bus terminal. Most of the bus companies' offices are at Jl. Sisingamangaraja No.155-159 and this is maybe the major point. (The office of one of the major Malaysian companies - SJS, is there. Tel. (0561) 734626,739544,765651.) Also you may check for info at Biaramas (other major Malaysian company) web page  after registration. There are buses in the morning and in the evening. In evenings the journey from Pontianak usually starts around 9.00 PM WIB (Waktu Indonesia Barat - Western Indonesian Time) with all buses traveling in convoy, the journey is comfortable as drivers are driving moderately. Reaching the border check-points between 4.00 - 6.00 AM WIB (with one or two rest stops in between) just as the checkpoints open their gate. The journey from checkpoints to Kuching is another 2 hours at moderate driving, reaching Kuching regional bus terminal at 7.00 - 9.00 AM Malaysian Standard Time (1 hour ahead of Western Indonesian Time).
Buses from Kuching regional bus terminal to Pontianak leave on two schedules, Economy class leaves at 7.00 AM and 1 PM Malaysian Standard Time, while Super Executive class leaves at 11.00 AM Malaysian Standard Time.
This is a usable itinerary. It explains how to get there and touches on all the major points along the way. An adventurous person could use this article, but please plunge forward and help it grow!