That's likely an OEM copy. Cheaper, but with a few caveats. You can't transfer the license to another computer, so once you activate Win7, it's locked to that specific system. It also comes with NO support from Microsoft. Granted that may be nothing new, but it's one of those things to note.
I purchased the upgrade version of Windows 7. It is currently listed for about $75 cheaper than the NON-upgrade version (newegg).
I upgraded from the RC two days ago (stupid Best Buy took FOREVER to mail me my pre-ordered copy), and I never needed to prove that I previously owned a copy of Windows.
I had previously owned XP, so I was prepared to enter that Product Key, but I was never prompted to do so.
So if you are considering getting win7, but for some reason you cant get the upgrade version, and you want to save some $$$....
Looks like you can simply install the RC (if you can get your hands on a copy)... and then install the upgrade version. Ta Da!

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