Im having the same problem! My motherboard will run 1333 and 1066 but i accidently bought 1600 ram......... It runs but my computer will randomly restart every now and then and I suspect this is why... But I dont know how to underclock it.
Yes you can run 1600MHz memory in a motherboard which only supports 1333MHz. This is because 1600MHz is the maximum clock speed that the memory is rated at, therefore you can happily run it at 1333MHz.
Just set the RAM at 1333MHz, there should be a DRAM:FSB setting or something similar some where. Just look for it, it should be on the page where you set the FSB.
Hope that helps.
beitzel15 please note that the advice I said was for your Core 2 system not your i7 as I didn't know. Refer to your thread for my post.