And the second disk in the RAID array failed again. Ack!
I took this as a hint. So I've now removed the old hard disks, turned off the motherboard RAID, installed the new SATA RAID controller, installed the pair of 400 GB SATA hard drives (removing the slow-down jumpers from them), and have installed Windows XP Professional.
Which I'm now updating to Service Pack 2. And pulling down all of the security updates.
After which I can reinstall the software that I need for mixdown.
If I'm lucky, I'll be back to mixing some time tomorrow.