will give you the the RTM version number, if it remained the same version number it wouldn't be an upgrade.
However upgrading from the RC, puts all your files in a Windows old folder and programs will need to be reinstalled, your data files can be restored from that folder.
If you have Vista and wish to retain your programs, you are better off to upgrade from Vista to the W7 RTM. There is less then 3 months to wait.
If you want to try W7 RC you would be better off to install on a seperate partition, giving you a dual boot.
I suppose this isn't only for windows 7, but its the context of this question.
I've been following the leaks of windows 7 (reading about, not downloading of course), until it has now finally RTM'ed. and i have one question. if i install the RC, (7100) and then run windows update, does it make it version 7600? or will it always be worse?
i do understand version number system. each change they make to the code makes it a different version.