George Kravis

BobT, I have the same camera and flash as you have mentioned, and have used it on similar occasions quite successfully. I set the camera on Program, aperture on f5.6, ISO 400 or 800 and shutter on 1/60. The reason for the relatively slow shutter is to give some exposure to the surroundings so that the subject is not isolated. The one major difference is that I mount the flash on an "L" bracket off the camera and I use a diffuser on the flash. That combination avoids harsh, high contrast lighting, thus producing more natural skin tones without red eye. The use of flash in that environment is necessary if you want realistic, natural looking images.

ralfstinson Loc: SF Bay Area

There is usually a practice session for such ceremonies, but if not, go to the church before hand see how your camera handles the light, and were the best locations are. Also think about white balance, you may want to put an amber filter on the flash to match the color temp.

Weddingguy Loc: British Columbia - Canada

Here's a very short video that should get you started in the right direction.
Would definitely suggest the use of flash. existing light is fixed and uncontrollable. Hope this helps . . .
http://youtu.be/S3IQFayyyoU