marzman, so what ya going to be running in your arcade, m.a.m.e for a guess and/or retro emulators ??
a few years i build my own tabletop arcade, used this site for parts - http://www.ultimarc.com/
the ipac (first version) on the site above was what i used to wire up the controls to the pc - http://www.ultimarc.com/ipac1.html
had a 1.3ghz duron cpu, motherboard with on-board everything, 1 gig ram, 80gig HD, 17" lcd monitor, worked like a charm