They're aware that I'm an amateur and I'm not promising anything; but they want someone to try and there's no money for a pro.
I used to do events, not the easiest... It's not art, just people grinning, some people are actually smiling because they are having fun.
Doesn't matter, they will still blame you if the "photo thing" doesn't turn out.
Head off to: http://neilvn.com/tangents/ for excellent info about bouncing...
Find out about the amount of people and the venue. Is this 50 people in a reception hall/church/restaurant or 5000 people in the convention center. Makes a huge difference. Go and take a look.
The easiest, but more expensive is to:
Medium-wide to medium-tele
1 flash with wireless trigger
Some soft box like a Lastolite: http://www.amazon.com/Lastolite-LL-LS2420S-Ezybox-Speed-Lite/dp/B00452V288
An assistant to do the "walking light stand", basically they move with you and hold the box at around 45° and about 3 feet from the person.
If the venue is small enough for bounce flash then use it, see Neil van Niekerk (tangents) for his "black foamie".
The other alternative setup: be at a fixed position with your camera on tripod, and people come in small groups to you.
The Business of Being a Photographer -- Lightroom Q&A