my P4-2.4Ghz machine does 9 tables (party beta) + PT (import every two minutes) + PAHUD + mp3 just fine.
Before operating systems got good at handling multiple monitors it was far better to get a single high-end card for them. Now I don't think it matters.
Parts shopping:
www.newegg.com
www.zipzoomfly.com
www.pricewatch.com
Caveat emptor on pricewatch but I can personally vouch for newegg and zipzoomfly