Yeah, it was actually pretty easy once i started to try it on my own.
Your seat belt locking sounds like the release pin (i think that's what it's called) is messed up.
When i bought the new ones, i tried to pull out the seat belt to give them a test, no go. It would lock instantly. But both of them did it so i thought they must have to be angled a certain way. Once i got all the panels off, i realised the angle they had to be out, and poof, no more lock.
Now, to get access to the seat belts, at least in my 00 here's what i had to do.
Step1. Remove the rear panel right above the two back seats (not sure what this is called).
Step2. Unscrew the seat belt (front) from the top, and also unscrew that little hook thing.
Step3. The top panel is now held in by those rubber screw things (so technical!). It had 3 of them, at least in mine, one at the back, and two along the wall right near the door. Once you get that off, you have access to the rst (rubber screw thing) of the big panel. Now, on the floor is a long strip of plastic, that just comes off by hand with a little manuevering.
Step 4. Pull down the back seat for the side you are working on, and there should be 3 more rsts. Making 4 in total for the larger side panel. Once you take them all out, the panel can be removed pretty easily.
Step 5. Now you have access to the seat belt mechanism. If you are replacing it, remove it obviously, but yours sounds like it might just be off a little, so take a look.
And that's it! First time i did it on the drivers side took me a couple hours to figure out what held what together and not to break anything. The passenger side took me 30-45 minutes max, full replace so it's not that hard. The only thing that proved difficult was getting the main panel back on, there's some insulation between it and the door that just didn't want to get out of the way. That might take you a bit to figure out. If you have any further questions on how to do it, post here i'll see if i can remember or help you.
And can anybody help me? For the 1000-2000 Rpm squeel? We took off the fan belt, it didn't seem to be damaged, and all the knobs turned easily. The alternator gave a little bit of resistance so we think it might be from that (if the problem is even there), thanks in advance! | 
