Here is a video I made on masking. It's just under 6 minutes long and is a quick tutorial on basic and reverse masking. I hope you find this helpful. I uploaded it on Google Video - I'm still trying to figure out how to embed it directly onto this post. This was my first attempt at using my webcam and my first try at any type of tutorial - so I was producer, director, writer, editor and star!! Please let me know what you think.
http://video.google.com/videosearch?q=masking_0001
http://video.google.com/videosearch?q=masking_0001