Unless the case is really great, just get a new case as it will not have all the problems of a proprietary case. I have several old gateways, and the cases will not fit normal psus and boards. I will have to take the dremel to them and do some work to get new stuff in there. The only reason I am doing this is because I like to do it, but most people will not have the patience for it.
Abit BP6 2X 300A@450 mhz, 1.5 GB PC133 ECC, Renditon Verite V2200, SB AWE32, Adaptec 2940U2W, 4.3GB Quantum Atlas 10K, Plextor Ultraplex