Earlier I had posted about "MSDN "How do I?" Videos" which were short 10- to 15-minutes "How-do-I" videos from MSDN which focused on specific tasks giving step-by-step instructions for using Microsoft products and technologies.
Here's one more of such excellent collection of webcast that takes you step-by-step to discovering new functionality or exploring a hot developer topic.
Check out : MSDN nuggets
And you can search for particular topic to get webcast on topic of your choice.
For example, here are the webcast from MSDN Nuggets on Silverlight.