What is the venue ? a home, a restaurant, a hall ?
The baby showers I have shot were in a hall, and I basically bounced off the ceiling all night and then when we did the group shots I brought out an umbrella on a stand with a 430ex, which definitely has sufficient power for this kind of job.
Something to watch out for: if the ceilings are higher than a couple of meters, still bounce up but throw a little light forward with a bounce card extending maybe an 1.5" or more up from the flash. You'll know bouncing straight up with no card isn't working when you notice raccoon-ing (harsh shadows) of the eyes.
Even while bouncing your flash I would plan on shooting the majority of the evening at ISO800 and somewhere between f/2.5-f/4. Drop the shutterspeed if you want to drag some ambient and create a sense of movement (especially during dancing sequence. Take a test shot, if there isn't an overwhelming amount of ambient in the image, open up a little more = longer shutterspeed).
Another tip: get in early if you can and photograph the details; it will be near to impossible to do so once the action starts.
good luck !