I have 2 hard drives: my C drive (primary IDE Master) is a 20GB drive
with the OS and apps; the Slave drive is a 120 GB IBM Deskstar with
documents only. (Spare me the anti-IBM hard drive stuff, I know I
should have gotten a WD.) As noted, they worked fine for a long time
on my old system.

But after transferring the drives, I couldn't get the new computer to
boot up, I kept getting a screen where the nice people at Microsoft
apologized for my inconvenience and offered to launch Windows in Safe
Mode, or the last known good configuration, etc. None of the choices
worked.

You *CAN'T* just move a hard drive from one computer and put it in another
and expect it to work. It *MIGHT* work for some, but definately a bad idea
to depend on it.

Back you data up to another location, move your drives an reformat/install.