I've been using an S5 IS for about a year and I'm getting an XTi tomorrow. I'm attending a 50th birthday party that I'll be taking photos at on the weekend and I would love to use the new camera. It will be in the afternoon in a church meeting room with big windows and lots of natural light coming in. I have a 430ex (and a bounce card if necessary?) and a 17-85mm IS USM. I'll also have an Expodisc to help with the color. I won't have a chance to really play around with the new camera before the party but I would really like to use it - any tips or suggestions on how to get some good shots with the new camera - should I just leave it on Auto and snap away?