i want to upgrade my dad's comp and get him Windows 7 Home Premium when it comes out, but there are 3 versions. here is what (i think) i understand and what i'm not clear on; OEM for System Builders ($110) - can only be installed on one configuration. a major hardware change will void it? Upgrade ($120) - must provide a key or cd from a previous version of windows? is a fresh install possible? can it be transferred to another machine later down the line? Retail ($200) - can install on as many differnt configurations as you want, but only one active at a time. also, if one buys 32-bit, can they get a 64-bit disc that uses the same key for a nominal shipping fee from MS?