Perhaps she's not a goner after all..

OK, so you put the car in gear and it doesn't move.
Is it an auto or manual?
Column shift or floor shift?
Your brother in law has a '75 Valiant, what are you working/having problems on?

When you put the car in gear and it doesn't move, does it try to move? Does it make any noises?
We can probably come up with a hundred different things to check, but if you give us a little more info we might can narrow it down some.
For instance, is your emergency brake on?
When you put it in gear and the car doesn't move, how much gas are you giving it?
C

Ah yes that might be helpful. This is for my own car, my 1976 Valiant, automatic, a904, column shift. I only mentioned my brother in law because he has a 75 Valiant and he was trying to encourage me to at least go out and take a look at the car...lol

My car doesn't try to move at all. There's no noises whatsoever, I know for a fact the emergency brake isn't on - I checked that before anything and I'm giving it a good amount of gas to move. When I put the car in gear there literally is no noise comming at all from the tranny or driveshaft, it's almost as if the car was in neutral except for the fact the idle goes down a little bit when it's in gear.

I really don't get it...AT ALL.