I had some problems too with the seat belt reminder too on my 04. If I recall correctly, your supposed to:
1. have key in off position
2. have your seat belt fastened
3. start the engine
4. within 30 seconds of step 3, unfasten and refasten you seat belt exactly 3 times quickly (within 10 seconds), ending with the seat belt fastened.
5. shut pickup off
If this isn't right, its in the owners manual. But be careful, the owners manual says to unbuckle and re-buckle the belt at least 3 times within a 10 second time frame, so I was doing it 4 times and it never worked. I then just did it 3 times and it worked on the first try (there was a post a few weeks back that also discussed the exactly 3 vs at least 3 thing).
I don't think there is a program thing to undo the chime on the key reminder. I never pull the keys from my pickup, but when I turn it off, I just pull the key out slightly from the ignition (just an 1/8 of an inch, but key still stays in ignition), and it won't beep (had to do this on GM's for many years). If this doesn't work for you, I suppose there is a wire you could cut to eliminate the chime, but I would want to make sure that the chime still worked if I shut the pickup off and left the headlights on.