Some of you may have seen this already, others may have not.  Below is a decent chart showing, based on what you have already (“Upgrade FROM”), how you can get to Windows 7 (“Upgrade TO”).

From All Things Digital

And, the folks at HowToGeek.com have provided some steps to do an in-place upgrade from Windows 7 RC to the release version (RTM).  And although I’m not officially endorsing it, “it worked fine on my machine..”  ;)