I have exactly the same problem with:
P4 3.06GHz
2GB DDR400
GeForce 7600GS
Before patch Y I had addons and all sorts (AA etc.), now on a fresh LFS install, no AA no AF, no texture addons, just a clean LFS install, 512x512 skins, low-res textures. A full grid on FE Club (well 20 cars) just doesn't work anymore. 10-20fps... unplayable.
No, spyware isn't the problem, no viruses aren't a problem, no I don't need to re-install windows (it has been done since patch Y), and yes ALL other games i've played are just fine. The problem lies within LFS since patch Y.