I'm having a slightly different problem. Brand new Athlon AM3 triple core with 4GB ram running Vista with a GeForce 260 GTX graphics card. G25 wheel. Just downloaded LFS.
The gas pedal is stuck full on, unassigned to any control, G25 gas pedal works the brake. I can't change anything. Set up the Logitech Profiler as suggested. No issues with GTR Evolution or GT5 Prologue.