It sounds exactly like my memory problems, I had to downclock/reduce timings to stabilise the system. In the end, the ram had to be RMA'edI hope the same is not true with you.
Strangely I had to do the same when I got Vista. 2 sticks of my supposedly "premium brand" Corsair memory were duff. Had to run Vista on 2GB for a couple weeks whilst the RMA went through

Won't be buying Corsair again that's for sure. Probably go back to me trusty old Crucial memory
