Now you can! Expression Encoder just released an update last month allowing VB developers to use the Expression Encoder 2 SDK. Here’s the announcement:
Expression Encoder is a tool for video encoding, and is a member of the Expression product suite. It allows you to import and encode video files, produce live webcasts, enhance media with watermarks and advertising, and publish with Microsoft Silverlight. You can learn more about Expression Encoder 2 on the product page here. You can also download the trial version for free!