Here's what DXDiag says:
BIOS: Phoenix - AwardBIOS v6.00PG
Processor: AMD Athlon(tm) 64 Processor 3500+, MMX, 3DNow, ~2.2GHz
Memory: 1024MB RAM
DirectX Version: DirectX 9.0c (4.09.0000.0904)
I don't know if this is relevant or not, but on the DirectX Files tab it has a little triangular exclamation point icon next to d3d9d.dll, and it says at the bottom under notes:
The file d3d9d.dll is a debug version, which will run slower than the retail version.
My video card is an Nvidia GeForce 8800 GT, and I updated the drivers for it just last month.
It was running pretty well in beta 1, but in 1a these framerate issues have shown up.