What I had not accounted for was that I'd switched from an AMD chipset to an Intel chipset and that the RAID mirroring on the motherboard isn't quite compatible. When the Intel chipset told me it would wipe out all the data on my old hard disks when I created the mirror, I decided not to take a chance and see if it was lying.
So I now have two new 1.5 TB drives installed in the machine. Once I get everything back together, I'll drop one of the old 400 GB drives into a eSata carrier and punch all of the data onto the new box.
I love technology. :)