Windows 7 - Windows 7 won't install on partition

I'm trying to install a fresh copy of 7 RC onto a separate partition on my hard drive. Everything will go fine until I select the partition. This is the message that pops up above the next button:

"System was unable to create or locate an existing system partition. See setup file log for more info."

I don't know why it's popping up this message. I create a new 50GB partition in Vista (per Vista forum) and formatted to NTFS. Am I suppose to right click and mark as an active partition?

I have ACHI enable in my bios. I've also disable that and still a no go. I had 7 beta on with no problems.

Update #2: So I redownloaded 7 and burn it again at the slowest speed, still a no go.

Update #3: So I try to install 7 RC from within Vista. Everything checks out and it will let me select the partition that I want to install it on. I did not know that you can install a new OS onto a new partition from within Vista. So install is going as planned.

Are you going from x86 to x64 or vice versa??
I installed x64 7200 on a previosly x86 and there was an 8gb partition and the other was the balance of the 1TB drive.

It would allow me to try on the 8gb partition but said that it was too small.....duh.

The option to partition the larger was never an option.

I was going to reinstall x64 on x64 to see if it would then but couldn't bother right now.

Yes, it is x64 to x64. I got it to install but now my video card doesn't work in either 7 or vista. It was working before in Vista.

Update 2: That blows, my DVI cable is bad. Now I need to find that receipt.