I just assumed the rumors were true that there was no upgrade path from Win7 Beta (Build 7000) to Win7 RC (Build 7100) and decided to use the trick the Win7 Dev Team wrote up on their blog entitled Delivering a quality upgrade experience. Sure enough, it worked like a champ! Win7 RC installed just fine.
You’ll need to either mount the ISO you download, copy the contents of the ISO to the hard drive using UltraISO or something similar, or burn the ISO to DVD then copy it the HD to make the modifications explained in the article. Getting the content ready takes longer than actually making the file change. Was the installation simple? You bet. But just like any installation, it does take a while so enjoy a game of Call of Duty: World at War or something while the stuff copies, installs, reboots itself, etc.
Check it out. You’ll be glad you did.