have you updated to the latest version? If you're running the basic 18.104.22.168 it won't work in XP
I'm running 22.214.171.124 in XP in D3D and it's fine, I don't think it's even in compatiblity mode.
Having said that I did get "stuck" in the lift at the end of 'We've got hostiles' - managed to get around it by switching to software mode until I was out of the lift, then back into D3D - worth knowing in case you get the same problem
Windows 7 x64 Ultimate Edition, Gigabyte Z77-D3H, Ivy Bridge i7 3770, nVidia GTX480 1.5Gb, 16Gb Corsair 1600MHz, Creative X-Fi, Seagate 500Gb SATA II, DGM 23" Widescreen TFT
"Men never do evil so completely and cheerfully as when they do it from religious conviction" -Blaise Pascal