There is a non-profit company in many North American cities that takes old computers, puts them through a testing cycle, recycles all the parts that can't be used, and then builds workstations running linux for either donation to non-profits or cheap resale. They are great and always looking for help.
http://www.freegeek.org/
According to the Wikipedia site, they have locations in:
Portland, OR; Fayetteville, AR; Central FL; Chicago, IL; Columbus, OH; South Bend, IN (Michiana); Vancouver, BC (Canada); Seattle, WA; Minneapolis-Saint Paul, MN (Twin Cities); Toronto, ON (Canada); Providence, RI; Ferndale, MI (Greater Detroit area); Ephrata, PA (South East Pennsylvania); Athens, GA (Free I.T. Athens)