Not true.
Running PJ64 on a 450 mhz AMD with Voodoo 3 card, XP.
Fast, no problems graphics wise.
Sound though, f****d on all emulators, same problem on each one, tends to repeat itself, echo.
The specs quoted for use are way too high on most emulators (with the exception of Nemu, which runs like an asthmatic snail).
My only piece of generally crap advice would be to turn off any crap that you have running in the background. I'll post the plugins that I'm using for each emulator when I get home, and this might help you too.
Best wishes, hope this helps.