Either upgrade Vista (if you are going from 32 bit to 32 bit version or 64 to 64 bit) or do a clean install of Windows 7.
If going from 32 bit to 64 bit a clean install will be required in any case.
Windows 7 RC1 is not a valid upgrade path and not recommended or supported by Microsoft.
Its almost always best to do a clean install.
I know its more of a pain in the ass, but theres allot of free software that can bundle your programs together to make the re-installation easier. Just google them, or perhaps search download.com for them.