Fixmbr and fixboot are XP commands (form XP recovery console) and they should be used on your SATA HDD 0 (where the XP is installed).
Did you try Bootrec.exe tool in Vista Recover enviroment? That is the tool you need for your other drive.
If none of this helps, the only solution would be to zero-fill the sector 0 with SeaTools for DOS.
If that tool doesn't help, try PowerMax. It might help, but it is ment to deal with maxtor drives (that Seagate took over), but who knows..
Both come in a form of bootable CD image, ready for burning, so you don't need an operating HD to run it, and both can zero-fill the whole drive (or just the first sector where the MBR record is kept).