You cannot tell for sure unless the computer is running and you can run the report listed in announcement 1 above.
The chances are that you have purchased a counterfeit copy if you bought it off of eBay for a significant discount. You may be able to tell by looking at this video
http://www.youtube.com/watch?v=hzqNNiOM0cs
The majority of Windows 7 offered on eBay, Amazon Marketplace, and other discount websites are counterfeit. They are very authenic looking and sealed but were manufactured in China and contain fraudulently obtained MSDN product keys that are blocked
by Microsoft once the abuse is detected.
Purchase licensed software like Windows, Office, Create Studio, etc. from the manufacturers or a very respected company like Amazon Corp.
Colin Barnhorst Windows 7 Ultimate x64 on DIY with 6GB ram.