As the RC version is officially available from MS's web site I would recommend that you download and install that one. As far as I know the official version is just called RC (not RC FINAL).
Also check the ISO file's hash values. For the 64-bit version these should be:-
CRC32: 58FB2BE0
MD5: 98341AF35655137966E382C4FEAA282D
SHA-1: FC867FE1AB2E0A9796F9E4D155B44EA6998F4874
To check these values download Hash Tab 2.3.0 from
http://beeblebrox.org - install it and then check the file properties - you will see a new tab called 'File Hashes' - you check the values from there. If they are any different I would suspect the ISO file which you downloaded.
Unfortunately I don't have the hash values of the 32-bit version of Windows RC - perhaps somebody who has downloaded the official release from MS can check the values and post them here.