I want to access the webcam so I can do some precessing on the images, like tracking a light, but I can't find a way to access the webcam. I googled it but I got confused.
Can you point me to a library that can do that (windows)? and maybe also provide an example?
I would need to periodically get a pixel map of the image, about 20 time per second or so if it would be possible.
You need DirectShow. This is a Windows framework for video playback and capture.
It's included in Windows SDK and there are many samples for video input capture included.
But, as Vijay mentioned, you can also try using OpenCV since it not only abstracts away the platform-specific video capture API, it also includes many image processing algorithms you could use to track the light in your project.
If you target Windows Vista (or Seven), there's the new Media Foundation SDK, which is slightly easier to manipulate and more feature-rich, and most important, will be better supported by Microsoft in the future.
You can find out about it here.
And about video capture specifically here.
Checkout OpenCV. It is a cross-platform computer vision SDK and has modules to capture images from the webcam. Maybe too feature rich for you, but it's worth a look.