Just a simple comment about live view mode. My XSi is only 3 weeks old. I used Live View 2 times. It helps if you are trying to get good focus on a closeup. My other posts discuss my problems of not getting good focus in AF mode. So I tried Live view since it has a feature that allows you to go into MF mode in Live View and Zoom the image on the LCD to 5x or 10x and then you can adjust the Manual Focus ring to make sure your LCD image is exactly in focus.
The problem is that the manual focus ring is so sensitive that a turn of 2-4 degrees will screw up the focus. It has terrible resolution. I doubt if I ever will use it again. Who knows it may work better when your driving a PC screen.