I just picked up an arcade cabinet (an old Zaxxon converted to a Skull and Crossbones) for my emulation project, cleaned it up and am ready to buy a 2nd computer to put in it and start playing. Its been a long time since I bought a new computer and was just wondering what everyone is running and what kind of performance you get out of it. Any suggestions for a new buyer?

The computer I'm running MAME on now is a Pentium 4, 2.4ghz with 512mb ram and I seem to get pretty good performance out of it. I see some slowdown on some games but the bigger NeoGeo games seem to run just fine so I'm looking for something similar to what I have now. Thanks!