The easiest way to do this is...
Search online for the "Windows 7 Loader" program. It is completely automated and will automatically give your computer a valid activation key. I think that the version that I used (as a test, of course) is version 1.7.7.
Following three simple steps now you can get rid of the pesky and sometimes buggy Windows Genuine Advantage (WGA) notifications:
1. Reboot Windows in safe mode (hold the f8 key while booting and you will get the option to boot in safe mode) and then:
2. Open Registry Editor (regedit.exe) and search for wgalogon folder and delete it. You should backup up the registry beforeshand, in case somethiong goes wrong.
3. In your windows directory search for files wga* and delete them. when you search for wga* please don\'t delete wgapi.dll if you found. This dynamic link is not related with that notifications massage.
You are done!
Now reboot back normally and continue your work. Windows Genuine Advantage will not bother you anymore.
Note: Now it is not required anymore. You can do it yourself by carefully following the guide above.