If you do decide to donate to a school, make sure you talk to them first to see if the computers will actually be used. I have seen many cases where a compnay donates their old computers to a school, and the school just takes them out to the dumpster because they don't need them or can't use them. If the computers aren't too old, they also make great second computers for families so the kids can type up their reports etc.
Other options include using them for things like firewalls (look for CD based Linux firewalls), or a file/music server at home. You could see if your friends could use them for one of the above reasons. The firewall one will require a second network card, but those are cheap and it would give you a good firewall for less than a router.
goates