A P3-800 is seriously "ghetto hardware" as far as the MAME devs are concerned. MAME 107 targets about a 3GHz Intel processor (or the AMD equivalent). To get decent performance on a P3-800, you can try going back a bunch of versions to one where the emulation was less accurate and faster. Try MAME 90 and see how that performs.
Also, note that MAME 107 and up use D3D as the default renderer. This doesn't mean that they use 3D acceleration, but it does mean that you now need a somewhat decent video card. You can force it to use direct draw by using the "-video ddraw" command line switch, or by putting "video ddraw" in your mame.ini. I can't say whether this will help performance for you or not.