Rally Championship 2000 Multicore CPU Problems

[Cowsheep]

With a singlecore game runs fine under Win XP SP3, about 200 fps average.
With a dualcore, framerate starts at 120 and drops to 0 (yes, it almost freezes) within 15 minutes during a racing.
With a quadcore, framerate starts at 20 and drops to 0 within 30 seconds.

Oneprocessorlaunchtool does not help, manually changing affinity neither.
Win 95 or Win 98 compatibilty mode is also useless.

I have tried every version from unpatched retail till 5.60. Always the same problem. Cracks dont help, too.

What should i do in order to play it on my quadcore?