I am looking to install Boot Camp for Windows 7 Pro, but I'm a little confused by the OEM version and the upgrade. I know if I get the OEM version, I am stuck with Windows 7 on that machine. Meaning that I won't be able to install on other computer if I decide to take it off one machine and move it to another machine. Does this hold true for the upgrade? Another question about OEM and the Upgrade, are you limited to how many reinstalls you do. For example you change something in configuration of the system, i.e. put in SSD drive in the computer. Would I need to re-buy the OEM again? Thanks!