You can now download Windows 7’s Release Candidate (for free) from here – bear in mind that it’s not the finished product hence you need to make your own call regarding whether to use it with critical data – it is very unlikely to go wrong though it is a possibility hence you should consider keeping live data elsewhere or at least implementing a comprehensive/frequent back up regime.
The Release Candidate will be fully functional until June 2010 when the license will expire and you will have to re-install. If you’re already running Windows 7 Beta then you’ll have to perform a clean install – make sure you back up your data before doing so! There’s a detailed post here explaining the rationale upon requiring a clean install together with a word around for anyone who absolutely insists that they need to install over the top.
Jeff Alexander’s blog includes a great post that gives details and shows screenshots of Windows 7’s Release Candidate in action.