Yes, you can setup a dual boot config with 32-bit Win 7 in one partition and 64-bit in the other. You can't upgrade from 32-bit to 64-bit, you can only do a clean (custom) install.
That being said, 2 licenses would be required for the dual boot config (I believe) and I don't really see the point. 64-bit Win 7 supports 32-bit apps just fine. I suggest you go with the 64-bit version only and minimize your headaches.