First wedding shoot next weekend!!

I've been asked by a friend to help shoot her wedding next weekend. They have no official (i.e. paid) photographer, but have designated myself and 2 other friends as the "official" photographers. She designated each of us a specific area, mine being photographing the groomsmen. One other will do the formals, and the third photographer is in charge of the bridal party. The main ceremony, reception, and all other parts of the wedding will be shot by all three of us. Any tips on what to do with the groomsmen? Posing ideas or anything you think would help?!

For equipment I've got
40D
350D (Rebel XT)
18-55 kit lens (no reason to use, just have it along for backup probably)
50mm 1.8
Sigma 70-300 3.5-5.6
Sigma 17-50 2.8 IS
Yongnuo YN-467
Yongnuo RF-603 triggers
One lightstand & convertible 42" umbrella

Thanks!

I'd worry less about equipment and posing. Where most novices fail (IMO) is that they didn't have a plan for the day and their flash/lighting skills were insufficient.

Understand how the day will flow, think about what lenses or what camera settings you'll want during different segments, how will you set the camera and your flash(s) to light the reception, etc.

Posing isn't too hard if you don't try to overthink it. Get ideas that you like from other photographer's websites or the photo sharing section here. But worry much more about the plan and managing your lighting.