I'm interested as well. From what I've seen you don't have to even have to have an SLI bridge between the cards. I've seen some having a GTX200 series card with an 8800GT or 9800GT for physics. Which makes me wonder if a person could use a Nvidia card for physics and perhaps have a ATI card as a main? (I know that you need an Intel or AMD chipset for Crossfire and an Nvidia chipset for SLI (With the exception of the X58 chipset) but because the cards aren't hooked together for one to run physics, I'm just wondering If you need 2 Nvidia cards to do this)