Booked my apt. with the Genius bar last night and hauled my MacPro up to the Apple store this morning. Explained the situation. Told him I did all the work already and if they just want to replace the OEM drive, I'll put it in the 2nd drive bay and leave the one I bought as the startup disk. The Genius went back to discuss with whomever, came back out after fifteen minutes... said they didn't have a replacement drive but they could give me a replacement MacPro.
So thats what we did. I lost a bit of data but nothing that important. Hopefully I have better luck with this new box.
When I put my other drive and ram back in, I'll take a look and see what this OEM drive is.
(Edit: The drive in the new (2nd) MacPro is a Western Digital WD Caviar SE 3200AAJS/320GB)
Overall, this system seems a little snappier than the previous one with the bad Seagate... of course it could have been that the drive wasn't right to begin with.
Oh well, a fresh start.