Even though Microsoft’s official stance is that you can’t upgrade (in any way shape or form) from the Release Candidate to the RTM/Retail versions of Windows 7, it’s actually possible to do so using a quick, easy 7 step program (hehe! 7 steps). This means that you can upgrade your RC version of Windows 7 Ultimate. If you don’t mind the risk of potential headaches down the line, you can do an in-place upgrade from Windows 7 RC to (Window 7 YOURRETAILVERSION), (as long as you remain 32bit or 64bit) RTM. Here’s how to do it, in 7 simple steps!
By the way to make a bootable USB drive, it must be done from within Vista or Win7 (32bit or 64bit) depending on your Upgrade retail version. (But, RC was free, and it will help us fix it's own shortcomings!) Beautiful!
Step 1
Insert your Windows 7 retail disc into your DVD drive. Make sure to put the 32-bit installer disc in if you’ll be installing 32-bit Windows and the 64-bit installer disc in if you’re installing 64-bit Windows. If you downloaded an ISO from TechNet, simply proceed to step two.
Step 2
Extract all the files from the DVD (or ISO) into a folder on your desktop.
Step 3
Open the folder you moved the files to, then open the “sources” directory.
Step 4
Using Notepad, open the “cversion.ini” file.
Step 5
This file specifies which versions of Windows are eligible to upgrade. Right now it says the minimum client version able to upgrade is 7233—change this to read 7000 and you’ll be able to upgrade the beta or RC to RTM.
Step 6
Save cversion.ini, overwriting the old file.
Step 7
Install Windows 7 using these modified installation files. The easiest way to do this is by following a boot from USB Drive guide (Max PC has instructions). If you want, it’s also possible to create a new installation disc from these files using the free burner ImgBurn. You can find a guide on how to do this by searching for "ImgBurn Bootable Windows 7" in Google. (Have not tried from the Desktop folder yet, but, can't see why that wouldn't work also?)
Now, even though Microsoft has intentionally made this possible (and spilled the beans about how to do it in a blog post), they don’t officially support this kind of upgrade, and they warn that it may result in “some oddities,” so proceed at your own risk. Still, I have had good results upgrading this way, and it’s a heck of a lot more appealing than paying full-price for a standalone copy of Windows 7.
OK... For those of you who read this far... 
Here is the magical Step 8 if you purchased a version other than Windows 7 Ultimate for your retail purchase... 
By default, it is not possible to “downgrade” the installed RC version of Windows 7 to a lesser edition. This is problematic, as the release candidate is the Ultimate version of Windows 7, while most users will be purchasing Home Premium or Professional. Thankfully, this too can be overcome.
To start, crack open the registry (regedit) on the release candidate box and navigate to the HKLM\Software\Microsoft\Windows NT\Current Version folder. In the right-hand pane, there are two registry entries named EditionID and ProductName.
Edit these registry entries to report the retail edition of Windows you intend to upgrade to. For example, users looking to upgrade the (RC) Release Candidate to the RTM of Home Premium would use HOMEPREMIUM for the EditionID, and Windows 7 HOMEPREMIUM for the ProductName.
Now that you’ve convinced the involved parties into accepting one another, the last thing to do is to start the upgrade. Simply run setup.exe from the retail Windows 7 folder on your hard drive (USB device or Burned DVD), and select upgrade when prompted.
Remember that Microsoft doesn’t officially support upgrades from the Windows 7 Release Candidate to the Retail or RTM versions. The firm has gently implied that, on rare occasion, it is possible for a system’s stability to be compromised as a result of an upgrade, so be sure to back up any important data before proceeding.
The entire process usually takes about an hour, but it could be much longer if you frequently use the My Documents or Program Files folders. When in doubt, let the installer run a little longer, and be sure to leave non-essential USB devices disconnected. When all is said and done, all you’ll need to do is activate to be on your way! The best part was that The Double Upgrade from Windows Vista (may it rest in peace) kept all Media Center Settings Including the ability to vary recording quality of TV to preserve precious Harddrive space!
Please rate this post if it helped you.
And since this is Crucial's Forum... Go get yourself some more memory!! 
Do I win something for the plug??
