The old STI shifters usually just get gummed up. Stripping them down and soaking them usually will free them back up...or if they aren't toooo gummed up shooting something like GT85 inside them will bring them back. If they are 7 or 8 speed, there are a few people out there who have all the small parts and will fix them for like 35 bucks each.

OP: sounds like you should be volunteering at a co op if you enjoy fixing old bikes back up! At least you wouldn't be spending your own money. I've been very fortunate to have a friend who workes in bike shops for years and has every tool out there...as well as a very healthy collection in various parts bins. He has been very free with giving me some real nice stuff (like cranksets, a dura ace brifter, cassettes, etc).