Fogold,
I tested one of my AMD/ATI computers:
AMD XP 2500+ (Barton) @ 2.15 GHz (200 x 10.5)
Abit NF7-S
Corsair TwinX512 DDR400 ram
ATI 9600 Pro @ 484/688 (344x2) Cat 4.1
AH2 Beta 13
1280 x 1024 AA x6 AF off, all other settings max quality.
Spit IX on runway through windscreen 52 fps
Lesser card (oc'd a bit) but more processor = more fps than you're getting. I think that confirms your XP 2000+ is throttling the 9800 Pro. For another $200 you could upgrade mobo & cpu and AH2 will be playable. Gee it's fun to spend someone else's money.

But this year is supposed to see some big changes in hardware, DDR2, PCIX, etc. so I'd wait awhile since everything except AH2 plays fine. I'm sure HTC will get the radeon issue in AH2 solved and you won't have to upgrade.