Well you can do what I'm doing. Build right now, with great parts everywhere except for vid card, which shouldn't go higher than $200 like mine. If you buy Windows XP MCE now, which is $110, and install it, an upgrade to Windows Vista Ultimate should more than make-up for the $110 you spend. Because if you bought Vista Ultimate and had no previous OS, it would cost probably more than $110 than just upgrading.
Then, ebay your DX9 card, and check out the r600. That's what I'm doing.
Stacker 830 - e6600 @ 3.6ghz - Eva 9800GTX+
X-Fi Xtrememusic - 4GB OCZ SLI 1066
Sceptre 20.1" - Logitech Z5500 - Gigabyte DS3 965p