I agree with Shy. The physics card is a waste. In fact, that 8600gts that you got would work for physics. As Shy said, nvidia owns Ageia now, so you can use Nvidia cards (8series or higher) as physics, and get the same effect.
Although, most of todays games don't support physics yet, so really no point in it.
(and just so you know, when you do enable physics, I see more load go on the CPU then.)