Microsoft are “giving away” Windows 7 to people. On the whole a good business strategy, but terrible for all those poor people who think it would be a good idea to “upgrade” for “free” (as in beer).
For starters, Microsoft will just be using you as slave labour to find all the bugs so they don’t need to pay internal testers as they should do. The benefit of which will be for their commercial product, and not something you will be able to use indefinitely for your time and frustration. Then after they’ve had their fill of you the product will be released and your “free” license will be revoked, forcing every user to stump up full retail price otherwise format their system in order to go back since we are all aware that “downgrading” is not allowed.
If you do insist on installing Windows (at all) or even Windows 7, please make sure it’s not on a machine which you value your data on, otherwise you will be charged a nice fee to retrieve it in a years time.