So, have have you Win7 Beta and would like to upgrade to RC?

Well, for any builds since 7000 (the official beta) the process was really easy and smooth. However, if you try to upgrade to version 7100 (RC1), you will find that the ability to upgrade has been disabled. For the reasons why, have a look at the very good Win7 engineering blog. Hidden in there you will also find what to do if you really want to upgrade.

1. Download the ISO as you did previously and extract it to a disk.
2. Browse to the sources directory.
3. Open the file cversion.ini in a text editor like Notepad in elevated mode.
4. Modify the MinClient build number to a value lower than the down-level build. For example, change 7100 to 7000. Save the file in place with the same name.
5. Run setup like you would normally from this modified copy of the image and the version check will be bypassed.

Personally I have found the upgrade to be very smooth, it will warn you which programs will break in the progress, usually a reinstall will sort that that out. Final note, if you are looking to get a long life out of your install, don't upgrade but do a fresh install. It will save your old setup nicely in a seperate folder for you so you can pick up relevant files from there later.