Seat Belts

[Titan]

This is hard to explain, but here goes...

The passenger side seat belt has the safty mech. on it where when you pull it all the way out, it locks itself and won't let you pull it out again until it has wound all the way up. Well, the spring in my belt that pulls it back down has crapped out and I can't get the belt to retract the full distance. So now the belt is stuck out, it's locked so it can't pull out, and it's limp and won't get sucked back in. I called the dealership and they said I was looking at atleast $200 to get it fixed. A few obsenities and a "click" later, I figured I would take a shot at it. I looked at the door where the plastic piece attaches to the door and noticed 2 pop-rivot looking things. I looked around else where, but can't figure out how to get the piece off to get to the seatbelt assembly (under back seat maybe?). If anybody has ANY information on how to fix anything relating to this problem, any help is appreciated.