|Ok, here's where I am to this point...|
Hard drive crashed, leaving message: can't find NTLDR.
I give to a friend who says drive not spinning...he installs new hard drive and OS.
Meanwhile, I take old drive and find logic board on web...seller says mask ROM on platter must match chip on logic board...best bet is to swap mask ROM 8-pin chip from my original as chances are slim that they are same, and they must match.
Take new board, swap chips, install, and drive spins but BIOS can't see it. In fact, if I plug in both drives BIOS can't see either one--but unplug old drive, and new drive runs fine--this is all regardless of Master/Slave/CableSelect settings on hard drives.
Old drive is 150GB partitioned into 2 drives, new drive is 320GB
Machine is 2003 vintage running XP Home