Eratic Video Performance

After installing a new mainboard and processor, for some reason I just can't get any games to turn in consistant framerates. Everything WAS working fine until I did a WinXP reinstall after installing a the processor and mainboard. Right now I'm guessing that in Medal of Honor AA, I am periodically getting 1 to 5 FPS, with it bouncing up to 170 FPS. This is running 1024x768, 32 bit and all the bells and whistles set to either high or medium. I checked and it does this online OR on a local server I set up, with no other players onboard (although it seems to do a little better).

Consider that I just ran 3DMark03 and turned in a respectable 4,664 3Dmarks. I notice a similar problem with SOF2, another game using the Q3A engine, and the thing won't even get off the menu in Battlefield 1942. Prior to the processor and MB change, the thing did about 3,700 3DMarks. So I'd be fairly certain that the problem is specific to the new equipment and/or the XP Pro install.
I also noticed that I get an occasional "stutter" when playing a DVD movie. This would seem to be related.

Here's my specs:

AMD Barton 2500+(333FSB) on an Asus A7N8X Deluxe MB with the 1.04 bios rev. , 768 MB of Mushin PC2700 DDR. Windoze XP Pro, SP1, DirX9.

ATI Radeon 9700 AIW Pro, Cat 3.4 Drivers. SB Audigy2 , latest drivers. Twin WD 80 GIG HDs (8MB buffer, not in RAID 0).

I don't know what other info would be pertinent. This performance is bad beyond tweaking, it's got to be something simple that I missed.

I had XP Pro installed when using a VIA KT333 type mainboard. After installing a nVidia SPP2 type MB, I fdisked, reformatted, and re-installed Windows XP from scratch on the HD, including installing Service Pack 1 and other updates as needed. I then reinstalled (similarly) all applications.