i am trying to figure out if i could put my old WD 320 GB Caviar Blue HDD (already has windows 7 on it) into a brand new computer w/o any failures.
Motherboard being used will be a Biostar Intel 6 Series mATX (LGA 1155 socket).
Windows does not like getting transplanted. The OS may go completely mad due to hardware changes, not sure uninstalling as many drivers as possible prior to transplant will be enough to dodge a re-install without complications.
Depending on how that copy of Windows got activated, you may (or not) be able to activate it in the new PC.