I have the same problem with my system:
i have everything switchen on high detail and the maximum i can get is 40 fps, but then i have to switch a few things off. With everything on i get avarage 25, thats not okay with me! And the PO is so high all the time. When i drive in the cockpit view with my ff wheel the PO is 130, on the start/finish 150-160! But when I watch a replay out of the car or cockpit view the PO is under 100 wich is okay! So what do I have to do to drive with PO under 100 with much detail and hight fps (40 or so) and a decent resolution.
I thought it the game would work well with this specs, but obviously it doesn't!!
My specs are: Athlon XP 1900, 1024 MB RAM, GeForce 3 Ti 200, ultra 160 SCSI 12GB hardrive, win XP pro