Again mafia10, don't answer questions you know nothing about. We know SLi exists, but he means two CPUs in SLi, not GPUs, which doesn't exist. You can have dual CPU motherboards (although that isn't SLI) but these are expensive, and are usually intended for servers rather than home users, they're not built with gaming in mind.
Only big expensive server motherboard carry dual CPU sockets. like sammorris said, its not for gaming.
It's not made for gaming because the performance benefits are useless in games. They are made to handle multiple cores but not multiple processors. So a quad core on a single processor chip will work in some games. But two dual cores, let's say, will not. Apart from the complete uselessness cost becomes a factor. Even if you could find a commercially available dual-processor board with PCI Express x16, it would cost in upwards of $1000(If I'm wrong, post links.) So unless you have about $4k I wouldn't even think about it =/
I think you can find them for three figures, but they're certainly not cheap. Suffice to say, don't bother.
