Possible Duplicate:
When installing Windows 7 or Vista, does the language, version, architecture (64-bit or 32-bit) or source (OEM, retail, or MSDN) matter?
I run three computers through one router. Do I need to buy a 3 licence version of Windows 7 software, or can I instal a single user version 3 times?
I mean, I have re-installed my own copy of Windows XP about 6 times, on different computers, all used by me, at the same address. So what's the difference?