airbag system info

I'm putting together a 2003 Focus that had the airbag in the right seat back blown. I put in the seat bag, and had the local dealership scan the airbag system. They said I needed a new Airbag Control Module, which I found (used) and installed, and also need a Drivers Side Pretensioner. What the heck is that? I can visibly see a pretensioning device on the passenger seat but not on the driver's. Just wanna make sure there not jerkin me around. You now how dealerships are. Thanks for any info on the subject.