I tried it with XP2000+, 1gig RAM and 9800 Pro 4.2 catalysts. Like you I got absolutely appaling frame rates in the 30's. Now, I know the video card is processor limited, but I was V dissapointed.
I can play Halo at 1074 x 768 no problem.
Only thing I did was port my AH1 settings file to AH2 to save me setting things up again, which may be an issue.
Anyhow, I uninstalled AH2. Don't think I'll bother again till it's done.