Trotterwatch is right. You have Windows XP, although an excellent OS for emulation, is a bit too good for your system. Your graphics card is excellent for N64 emulation- keep it, even though it's old, it'll work absolute wonders with the Glide64 plugin. If its PCI you could use it as a secondary card if you want.
If you want to upgrade your system, I'd get a decent AMD processor eg. over 1.2GHz and you'll be able to use PJ64 and 1964 fullspeed. AMD are fast and very cheap, so you won't have to pay too much for good performance.
192MB is a little low, so get another RAM stick, so that your total RAM is close to 512MB. I reckon a 256MB stick would be a good choice and not too expensive if you want to upgrade from 192MB. RAM is quite cheap.
You may need a new motherboard to cater for all this new stuff if you still want your old computer case, but you might as well buy a totally new comp and move the Voodoo card to it as a secondary card.
If you are buying a new PC, avoid integrated Graphics or Savage/SiS graphics. Any non-integrated GeForce or ATi will do, and you can upgrade that when you can afford to. Well, that's what I did!