If I were you, I'd get a "real" motherboard, such as the P5WD2-Premium (if you don't have plans for a C2D upgrade ever) or a P5B Deluxe and overclock that Pentium D 930 to 250x15.
And you can keep your current RAM and video card and be ready for Vista + DX10.
There's no need for a 10K-rpm HDD, you won't see any difference at all from a regular 7.2K-rpm. In fact, a Segate Perpendicular Recording will be just as good and remember that time-speeds are measure in milliseconds, not seconds, so no real gain there.
$229 ($200) for 150GB? I think it's best and least expensive to have a RAID 0 with two Segates HDDs ($160 for 2x 250GB HDDs) w/ Perpendicular Recording than a single Raptor and you'll still end up with $40 at least, in your pocket.
But then again, that's if you get a good Motherboard, otherwise......