I'd give it to Silva in the Second round by TKO.
I think Kimbo's got a good solid jaw, and has the power to knock out Silva. His problem is that he can only really unleash that power on a stationary target. Anderson Silva is NOT a stationary target, and will never BE a stationary target.
Silva has incredibly powerful, but more importently, precise striking. Kimbo can hit a man, but Silva is capable of hitting a man who's moving his head. If it came to just stand up Silva would win pretty much hands down.
However, Kimbo's camp isn't full of morons. They'll definately be looking for a GnP victory over Silva. Silva hasn't fought a large number of GnPers, and he CERTIANLY hasn't fought someone as large and strong as Kimbo. I'd be looking for Kimbo's camp to brush up on his wrestling, and do some more intensive BJJ training (To avoid, not apply.) With the strategy to get Silva up against the cage, and slam him to the ground and work the GnP from there relying on Kimbos size advantage to win him the match.
The Problem with that strategy is that Silva's specialty is Mui Thai, so no matter what Kimbo does to get Silva to the ground he's going to eat a few knees and elbows doing it. And you're talking about some of the most precise knees and elbows in the sport. And let's not forget, getting Silva to the ground isn't a guarenteed win either. Silva's a black belt in JJ (BJJ?) and Kimbo will definately leave an arm dangling for Silva to break, or what's more likely is that Silva will use his incredibly long legs to apply a triangle.
At the end of the day Silva has too many tools to defeat Kimbo. His striking is technically better, his conditioning is better, his speed is better, his submissions are better. Kimbos only advantage in the fight would be his size and raw strength, and Silva is simply too good to let Kimbo fall back on those things.
I LIKE Kimbo, and I look forward to seeing him in MMA, but the dude will need three more years of training before even thinking of fighting a guy like Silva and winning.