Here is how he does it:
- take fast screenshots of the desktop
- figure out what part of the image changed (when compared with the previous one)
- share that image via WCF
- push that info to clients
He has a PoC using both a Windows app and ASP.NET app (yes, streaming over the web :) )
Here are his amazing posts on this topic:
Note: on the topic of remote access this VNC# client library seems quite powerful