Ah, so much for the XP idea! You may have to use another emu, as you're quite a bit below the specs needed for PJ. Even if you manage to get it started, it would be too slow for most games. How about UltraHLE? If you have a Voodoo card, all the better. (still possible to use if you don't) You might be able to play a handful of games decently, certainly SM64 at near fullspeed at least.
If you really want PJ64 working, I'd suggest closing down unnecessary applications and increasing virtual memory as often games don't even start otherwise. If you have integrated graphics and sound, use the Jabo video plugin or Glide64 for a Voodoo type card, and no sound or Azimer's audio v0.3. Do you have at least Direct X 7? You need this for PJ64. If the message keeps up, then delete and re-download PJ64. Otherwise another emu.