Not guaranteeing it'll fit your needs, but with that many cores and that much memory you can probably afford to run XP in VMWare Fusion or Parallels.
Yeah, I used Parallels on my previous Mac, a Quad MacPro. It ran OK, I suppose, so I could do that. It’s certainly convenient enough, but it doesn’t claim enough RAM for itself to suit me. IIRC, it only accesses 512MB.
But now that I’m running Leopard, I have Boot Camp, so that might change things. I’ll have to noodle that for a while, poke around in Apple Discussions to see what the pitfalls are.