How to Install Windows 7 Guide @ OCC
 

The next step is very important but can be delayed. Windows will want its product key entered, which is included with any legitimate install media of Windows, in one form or another. You are able to skip entering the key at this time though, as I did simply because that key is already in use for my desktop, which is also why it has been told to not attempt activation. There is a 30-day grace period to enter the key through System Properties before Windows ceases to function.

http://www.overclockersclub.com/guid...ndows_7_guide/