the only problems with a geforce3 is that you don't have nice opengl support under freebsd or most other unix platforms (maybey only with the accelerated x server (not a free x server)
http://www.xig.com/ is a site for an accelerated x server ). i don't know if it works under freebsd. if you don't need fast 3d supprt you could use the software 3d support from mesa .