Well I got an indentical (except it's 20gb) drive. Works fine in the
PC. Swapped boards and neither will work.

Because they're not identical. It's not a case of 'almost identenical' or
'pretty close', you need an *exact* match to the make, model, capacity,
revision, etc of the drive for it to work.

This is bad I guess as it
means both the board and the motor/heads/etc are mangled. Nothing for
it now except try to crack them open and swap the platter I guess.
Wish me luck boys, I'm going in.

I hate to sound pesamistic, but all you're likely to do is destroy both
drives entirely in the process. For starters you require a cleanroom
environment to even open a drive (the space between the heads and the
platters is in the range of hundredths if not thousanths of a millimeter, so
a single spec of dust can cause irreppairable damage).

Even if you had the right facilities, you would still only be able to swap
platters with an identical model - but that's a moot point because if
everything was identical you could swap the boards anyway.

Chris