It's not SLI-ready, few good Core 2 Duo motherboards are.
The good ones use Intel chipsets, which do not support SLI. You'd have to get an nForce-chipset mobo to get SLI, but I hear they're not good overclockers. In my (humble) opinion, SLI is not worth it anyway.
Also, I just recently bought a P5B-Deluxe, but it hasn't arrived yet. I'll let you know my opinion of it once I get it.