personally Im waiting for the hammer to be released and stable with good boards and such till I upgrade, but if you want here and now, I would go high end XP processor. 2000+ or higher IMO. just because you chunked down the cash for that kinda vid card you should back it up with one kick ass machine.
here are my specs for a kick ass rig.
EPOX mobo (forgot model # but it has onboard IDE raid)
2200XP
Your choice of sound card (I go SB but thats me and there are better and worse out there)
512MB Ram
2x or 4x maxtor 80 gb 7200RPM HD's
Pioneer DVD (I prefer slot load)
Plextor CDRW (fastest availible)
Sony Floppy drive (ya ya no one uses um until you use them)
and a 19 inch sony trinitron monitor