Problem:

"Windows could not determine if this computer contains a valid system volume"

I had booted Windows Server 2008 RC, loaded my RAID (3Ware 9650) drivers from USB stick, and created a partition and formatted it.  I go to install, and Windows stops dead in its tracks.

Solution:

Leave the stick plugged in, reboot the system, and go into the BIOS and REMOVE the stick from the boot order entirely.  Ensure the RAID array is 1st in the list, and give it a try again.

See also:

After I discovered this, I also read these websites, which I thought might be useful...
http://www.nforcershq.com/forum/vista-and-nforce4-sataraid-an-installation-guide-vt66299.html
http://www.dashken.net/index.php?/archives/204-Windows-could-not-determine-if-this-computer-contains-a-valid-system-volume.html#extended
http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=2201257&SiteID=17