Forum:(PC)Borderlands uses only half of CPU power. Need help.

I have mentioned that Borderlands always uses no more than 50% of my CPU power (in process manager), that explains why its running much slower than Batman: Arkham Asylum that was made on the same engine, but uses 85-100% of my CPU. My suggestion is that BL somewhy uses only one core of my Core Duo. Does anybody knows how to fix that and force BL to use both cores?