the problem with social events is it's a social event not a photoshoot and the best you can hope for is a few photo's of people having fun
thyere not really there to pose for a camera and every thing is stacked against you the lighting is all wrong your using a single flash and to cap it all the people there arn't that interested in you pointing a camera in their general direction ( thats untill theyv'e had a few and are in no fit state any more ) so the best advice i can give is catch em early and get the photo's
try and bounce the flash so the lighting isn't as harsh if you've got a diffuser use it if not botch one together a piece of milk carton will do

it will make a lot of difference to how your photo's turn out
the camera settings i would go for ISO 100 around F8 and 1/60th shutter speed to catch as much ambiant light as possible
as said by emily16 keep the iso low ( 100 will be fine ) to minimise noise because there's gonna be a lot of dark areas in your photographs and any noise will show
at the end of the day it's something your gonna have to experiment with a good idea is to go outside in the dark and take a few photo's with the flash and see what works it will give you an idea of what to ecpect in a big room ( sort of )