Front converter is the front warm up(pre) cat. I'm kinda with Doom on the DIY. The pre cat and the O2 should be no problem. The airbag and wire assy would make me think twice, but if you're up to it...rock on.
EDIT: You may want to check that front pre cat first. It's either going to be between the manifold and the y-pipe, or it may be integrated into the y-pipe. If it's the latter, you could just buy an aftermarket y-pipe depending on how strict emissions testing is in your area.
Check out these guys for OEM parts at considerable savings. Great service.
http://www.nissanparts.org/
You may want to try
http://www.car-parts.com for an airbag assy. Keep in mind any shipping on that part will have to be via ground.
Do the notes on your repair order happen to say what is wrong with the air bag and wiring assy? That's not something that is very common.