EOS Camera Movie Record is a neat open source project to enable video recording with the Canon EOS 450D/Rebel XSi. Before you get too excited, there are a couple of caveats: no sound (of course, the camera has no mic) so if you want a video with sound you need to record it simulaneously through another source. Plus, the camera has to be tethered to a Mac or PC with the USB cable. But the video quality itself is pretty nice, 848x560 px at about 20 frames per second.
It’s a neat trick that just uses that live view function of the 450D to record. The Canon Mac/PC software that comes with the camera, called EOS Utility, can display the live view image on screen, just not record to file.
On that note, Canon really should give up their obsession about keeping their software under wraps. If you don’t install from the CD that came with your camera you have no official way of installing their software, and you have to resort to dumb hacks if for whatever reason you don’t have the CD handy.