Head over to silverlight.live.com to create yourself a Silverlight Streaming account key and begin uploading your Silverlight applications and media. Silverlight Streaming allows you to upload up to 4GB of media content, with videos of up to ten minutes in length. The storage is "in the cloud" and files are globally cached.

Here's a rough and raw walkthrough of how you can use it:

• Grab yourself the trial edition of Expression Media Encoder;
• Take a video and encode it - make sure you go to the Output tab and choose a player template;
• At the end of the encode process, you should have a directory that contains the media file, some XAML and JavaScript files and any thumbnails that you've specified through the Markers tool-window.
• You'll need to remove any .html, .aspx, .media, .csproj or .config files from the output directory. You won't need these for the Silverlight Streaming service.
• Then you'll want to add a manifest that describes the Silverlight application; for a default player from Expression Media Encoder (I used the Glassy theme), you can use the following manifest:

<SilverlightApp>
   <loadFunction>StartWithParent</loadFunction>
   <jsOrder>
      <js>MicrosoftAjax.js</js>
      <js>PreviewMedia.js</js>
      <js>EmePlayer.js</js>
      <js>player.js</js>
      <js>startPlayer.js</js>
   </jsOrder>
</SilverlightApp>

• Save the manifest as manifest.xml and add it to the directory.
• Now simply zip all the files up (make sure they're in the root of the zip file).
• From silverlight.live.com, go to the Manage Applications tab and upload the application.
• From here, Silverlight Streaming will guide you through the remaining steps, providing you with the JavaScript and HTML code you'll need to add to your page to access the streamed content.

Check out the WPF Momentum video I posted a short while ago to see an example deployed in action.