I'm glad I came across this thread. I have been pulling my hair out trying to find an app that does just this.
My mate who has an x-box mentioned that the x-box live facility has an Iplayer plug-in that extracts all media available on the bbc website and presents them as a choice of thumbnails for you to click on and view. Apparently several other plugins service other sites. Also apparently it is written in python.
There is an old thread here...http://xbmc.org/forum/showthread.php?t=27063
and they have it working now.
I have extensive safety critical software development knowledge and dable with perl etc, and I would be delighted to get my hands dirty doing such stuff. Problem is I don't know where to start. There is mention of XULRunner and XPCom so I'll be reading up on these.
Cheers for now