I looked into those intensive language schools once...there is a great one in Costa Rica that is part eco-tourism and part language school, on the edge of the rainforest. I could probably dig around my paperwork and find the name of it if you like, though I'm sure you could find it online.

If it's still in print, there's a book out every year called _Volunteer Vacations_. They list a plethora of trips...everything from archeological digs to medical missions, etc. (Most of them are dirt-cheap, too!)