I wonder if it is possible to use the Canon Powershot A3100 IS camera as a Webcam in Windows 7 PC. If that is the case, how can I proceed? Are there some recommended techniques?
No, this is not supported on any operating system.
I do not know of any recent camera to do that unfortunately.
PS: Some people have hacked Canon firmware to do things that are not supported. Whether it is possible or not, I do not know, but you can check this to see.