Thanks for the replies, but (and not to sound like a smart-ass), I already know all that.
What I asked is:
Can you build another person's credit on a card when you co-sign with them without them actually using the card?
Basically if the person w/ good credit ONLY has the card (don't give the card to the bad credit dude), can he then raise the other person's score?
The person with bad credit would never even TOUCH the card once, but since the other person co-signed, I'm assuming they could use it while simultaneously raising the other person's score. Is this correct?