Something has to be wrong somewhere. I run mame, snes, genesis/megadrive etc on a flexatx sized pc with the following specs
p4 era celeron 1ghz with no CPU level cache
512mb ddr1 pc3200
40gig 5400rpm drive
on board intel 845i graphics
I can easily play roughly 70% of games without ever touching a single setting.
Something may not be playing well with mame on that machine (no pun intended) Try a different mame derivative, check your cpu load and memory usage.