I know you can upgrade 32 bit to 64 bit using a custom install. My question though, is I installed Windows 7 32 bit using a retail upgrade disk. I've now decided I want to try 64 bit. Since the upgrade box contained 2 discs (32 & 64 bit), am I free to install the 64 bit on the same computer or would I have to buy a whole new upgrade disc set? It seems like it would let me install the 64 bit which would have it's own key, but I want to make sure.