Juan Santamaria Airport is located close to the cities Alajuela, Heredia and the capital San José.
The Interamericana (Panamerican highway) runs through Costa Rica and is the main entry point by car. The border post in the north (to Nicaragua) is called Peñas Blancas and in the south (to Panamá) Paso Canoas.
Spanish is the language used in Costa Rica, but in the tourist business, most people also speak fairly good English. If you look like a foreigner (most tourists do) people will usually address you in English.
Some Costa Rican expressions:
The local currency is Colón(es) named after Columbus (Spanish: Colón).
The rate of change is about 450 Colones for 1 US Dollar (August 2004), but note that there is a growing inflation. You may find the current value at this currency conversion site. Also note that the use of US Dollars is quite common, in fact, in the tourist setting, almost everything is priced in Dollars.
Gallo pinto is mostly rice and beans. You can get it to breakfast, lunch and dinner.
Hotels in Costa Rica are more expensive than in its neighboring countries to the north.
You can learn Spanish in Costa Rica, but probably a lot cheaper in other countries, like Guatemala. Also be aware that the Costa Ricans have adopted a slightly us-English pronunciation on a lot of words, so you run the risk of getting that too, even if you're from some place else.
A lot of the eco-projects are seeking volunteers.
The traffic is dangerous, so take care.
The international calling code/country code for Costa Rica is 506.