SB75G2, trouble with new seagate ST3120814A

Started losing my western digital WD1200, and got a seagate 120gig to replace it.
Did some initial partitioning and formatting and data copying to prevent losing it all, via external USB kit and mount... Largely because I could never get the drive recognized in bios when connected to either IDE (non-SATA) bus.
According to the system specs, it (my shuttle) should support ultra/100, yes? So why on earth is the bloody thing giving me such fits?
I've tried two cables. Both cable positions. Both IDE channels. Running it as slave on the channel with the DVD writer. Running it as standalone master on the primary channel (dvd on the secondary channel). Running it as slave to the Western Digital. All kinds of things.
It just doesn't (90% of the time) show up at all in bios when not run off the USB port. SOMEtimes, as I fiddled with cable, jumper, etc, it would show up in the drive list. But it never survived so much as a reboot to actually load an OS on. Seagate's tools get me nowhere (a prereq is having it recognized).
I even updated the shuttle bios to 01g, to see if there was a 'mode 5' option in the bios settings to match what Seagate was apparently wanting.

Any ideas?