I contacted Western Digital, and they gave me a rather generic reply saying that it "might" be possible but that I should confirm it with Microsoft.
Well, I'm gonna try asking here first. Any input would be greatly appreciated.
Having a single mirrored external drive with this much space would really be an end-all, be-all solution for the foreseeable future. I only have one eSata port on my computer, so getting two 1 TB drives like this just wouldn't be as slick.
I see this as more of a BIOS issue than an XP one and one issue will be will your BIOS allow Legacy Support to USB devices. I think there would be problems with the RAID array if any part of it was missing at boottime. Is there a BIOS update available for your system?