*note* this works for canon A70 but should work for other cameras that are compatible with Canon RemoteCapture software.
1.Download the free manycam software from http://www.manycam.com/
2.Download remote capture software from canon website href="http://software.canon-europe.com/software/0019052_0000578.asp?model=
3. Install both pieces of software.
4. Start Canon RemoteCapture software. If using windows 7 or vista you must setup up the Remote capture software to run in Windows XP SP3 compatibility mode. Plug the camera to your PC with the USB cable, set the camera in review mode(the mode for viewing taken pictures), and then turn it on. In the Remote capture software click on connect. If all works OK a new dialog should open titled Shooting - Remote Capture. Click on the arrow next to "detail setting" to expand dialog. Now there should be a blank panel and a button saying viewfinder off. click viewfinder off button to turn it on. There should now be a live stream from the camera displayed in the dialog. There are also plenty of setting to change to optimise the image.
5. Open manycam software click on source->desktop>custom-desktop place the target window over the camera live stream from step 4. Click close on the target window once it is matched up correctly.
6. Done, you should now have a decent quality webcam from just using the camera, usb cable and free software.