I've removed the WD drive from the NAS, set its jumpers to operate with 512byte sectors and installed it in my XP system. I'm backing up the NAS onto the WD and two additional 1.5TB USB drives.

Then I'm going to start with the NAS from scratch. I'll feel much better about figure out performance issues once I have everything backed up. Once that's all settled (fingers crossed) I'll put everything back onto the NAS.

The only thing making the copying anything close to sane, is Teracopy, which Matt had recommended and mentioned a number of times last year.