providing 56k isps?

this is a project presentation:
is it possible to provise public isps using my onw 4mbs connection? iv done some reserch and still not sure. my thought is to use my XP pro unit as a RAS or upgrade to 2003 server. im still not sure how this would work. (or if its even legal as a project)
how would i go about setting this up if possible?