right. I couldnt get any W7 build to install from the DVD!
I have lots of drives, all SATA, and I did a clean install from desktop and things are ok. As long as your wannabe C drive is physically connected to the lowest SATA port number, ie Sata 0, rather than having them rearranged within the BIOS ordering everything should be cool. In your case with RAID you want either your two raid drives as 0 and 1, or to unplug all other drives so that the only drive windows see's is your RAID stack and as such it gives it a C letter.
If I were you I would unplug all your drives other than your RAID stack, install Vista x64 with minimal drivers then try the clean install of 7100 from the desktop. I know it's a chore but I think it will work as I have a misplaced trust in MS's technical ability.... once it's up reconnect all your drives and then messa bout for ages switching the boot order in the BIOS inorder to get W7 to boot again, as this always seems to happen.
If you don't want to do that then I would examine the Vista x64 inf file for the raid drivers in notepad and see if you can see anything which looks out of place and wouldnt thus function in W7.
Good luck - it will be worth it in the end!