And when you try again, let it sit there a good 10 minutes. The first time I installed the RC, it waited about that long and then moved on.
Once it was up and running - and it did eventually get there, a look at the device manager gave a clue. There were a couple of h/w items missing drivers. Maybe Windows 7 was just waiting for the timeout and it had to do this multiple times.
With more recent builds (currently using 7227), I no longer have device issues as the drivers in the build are "good enough" to get through the install. I do, however, have to visit Nvidia for a video driver and update the NIC h/w driver as well.
So, start the install go grab your a cup'o or something.