Things like Office look at the hardware in your computer (serial numbers, the MAC address of your Ethernet card, etc) to come up with a unique hardware profile (for want of a better description). There won't be a problem entering your serial and the hardware profile will be the same from your previous install and the W7 one, so activation shouldn't be an issue either. Even if there are activation problems, you just call up Microsoft and explain what's happened and they'll activate for you. For MS products like Office, serial numbers are validated inside the installer only - no internet connection needed.