Just bought myself a nice Canon SD750. I'm having an issue with the video files. They record in .avi but there seems to be no codec to play them on a computer (or to edit them in imovie for that matter). There also doesn't seem to be any resources to explain the situation on the canon site.
FWIW, Canon records using Motion JPEG which is supported by QuickTime just fine (And plays in VLC as well). They just use an .avi container. Personally any movies taken with a Canon camera I recompress to H.264 after to save space largely because the audio is uncompressed.