Thanks for all your help [British mode]lads[/British mode], but like I always do, I went with the nuclear option. I love puttering with hardware, but nothing frustrates me more than software. I tend to reformat when faced with any kind of problem. But it worked this time!
I installed over XP on it's native C partition, but it seems something from the D or E snuck back in. Just to see if Battlefield 2 didn't really fudge up my hardware, I installed XP, Direct X 9.0C, NVidia 77.30 drivers and Battlefield 2 on a 250GB Hitachi IDE, and it ran fine for awhile. I installed Half Life 2 to continue tests, and things got squirelly. I went ahead and reformatted my SATA 250s, and so far everything's good! Half Life 2 runs like silk, and my PC laughs at Command and Conquer Generals, oh and Battlefield 2 runs fine as well.

3 reformats and a bunch of cautious installs later, things seem to be stabilized.
