KP, you can take some nice shots with that XTi. No worries there.
Like Fug wrote the filter probably won't do you any good. Shoot raw and you can adjust in post processing. Once you get the hang of it, you can make the adjustments rapidly and once you adjust one raw in a series, you can apply the same adjustment to all of the others. If you have to shoot JPG or it's your absolute preference, learn to set the white balance manually. Carry a piece of photo paper or other white paper (poor man's method, you can also spend money on a grey card) and use the techniques described on page 86 of your manual to set a custom white balance. Essentially, you take a picture of a white object (the photo paper or a grey object the grey white balance card) filling the view finder. It doesn't matter if it is in focus. Just take the picture in the lighting environment in which you will take pictures. Then just follow the steps outlined and you should get pretty good JPG images, although some lights cycle and you may still have trouble. You can get around it with RAW, but not as easily with JPG.
Randy, I hadn't thought of slowing focus tracking... Ugh, always something to learn. I know that's what's wrong with some of my photos.
KP, pages 57 and 58 of your manual tell you how to select your focus point. Set it to center point (the best focus point on your camera) and keep that little center rectangle over the hips or face and you should see some improvement. Unfortunately you don't have a way to focus separately from the shutter button, that I can see, so you'll have to go with this method for now.