When installing XP on a new non-RAID drive recovered 3/4 of my data on the RAID and let me rebuild the array to its original 4-drive fully functional condition, I saw that I was going to have to re-install all my applications. Since I would have to do that if I upgraded to Vista, I figured just save the painful first re-install and upgrade to Vista now.
I popped in the Vista 64-bit Ultimate DVD, and instead of it offering me an update choice, it only let me do a clean install. That's okay, I thought, I won't need all those old XP files anyway. So I blew away the XP partition and formatted it and installed Vista where XP had been. I also loaded the Vista 64-bit drivers for my RAID array and the non-RAID SATA drive which the OS would sit on.
Vista comes up seeing the RAID array, it even gave me the right file system type and capacity (just over 1 TB). But it would not let me open the drive. "Access denied". Even though the drive properties showed it was read/write.
So I wiped Vista and re-installed XP. The array magically was accessible again. And now I am feeling so stupid because what I should have done was make two partitions, and put XP on one and Vista on the other. Which I'll do when I get home tonight. Or at least start, until it's time to head for BASFA. I'll show up at 8 instead of my usual 7:30, because I've already seen frankwu's excellent animated video which will be tonight's pre-meeting entertainment.
I'm pretty sure all I need to do to get Vista to access the RAID array is to install Intel's Storage Manager software for Vista. Installing the XP version is what allowed me to rebuild the array back to a stable condition.