Updated Macbook Pro to Snow Leopard.. Why won't Starcraft II work?

I just updated my 15 inch unibody MBP from Tiger 10.4.11 OS to Snow Leopard,10.6. The systerm requirements say 10.5.8.. Snow Leopard is higher than that.. But even when I tried to download the SCII game, it said my system didn't meet the minimum requirements (said the operating system was out of date). How do I fix this??