I doubt it would be miss, my crappy laptop can handle all my mame games fine, main reason I want a desktop in there is svideo to use a TV instead of a PC monitor.
did'n tthe cab you bought have a working arcade monitor? just use that you dont need svideo out to hook up to one you can directly from the db15 vga port.
you said athlon 64 so im assuming it's a older single core 64, well even if it was a newer x2 you'd still need to OC It to play all games 100%
try out some of the 3d games on that system you'll see how badly it will choke try running mortal kombat 4, san franciso rush, or gauntlet legends by for example..
i doubt when you say your laptop handles all games fine you're actually trying to run the games im talking about, and im sure the athlon 64 can't.
im not saying that system wont be suitable.. im saying you should test the games you care about most before using it.. nothing will suck more then getting everything setup only to find you can't play a game you really want to.
if it's not fast enough for a game you wanna play then you have to decide if it's important enough to get a faster system or if you can live without it, but do this before you put the effort into setting everything up not after.