What I typically do with a TV display is I experiment with the Windows settings until I find the combination of resolution, color depth, font sizes, icon sizes, etc. that produces the most pleasing desktop display on the TV. Sorry but there is no exact answer to your question, it depends upon your card and driver options.
As for ffdshow, etc. I would not encourage you - the TV is a low resolution display and I seriously doubt that there would be any visible difference between what you propose and simple overlay display. Some boards that do particularly good overlay (like the old Matrox Dualheads) have significantly better fullscreen overlay displays than they do Windows desktops - at least they do on a TV.
At best a standard TV is blurry and the best of them (like my Sony Wega) are barely usable as computer displays for Windows desktop. Nevertheless the overlays can be quite good on such displays using video material. For TV display the oldest PC video solutions (Hollywood+ and X-Card) still rgularly outperform any combination of software. If you are really serious about Divx on a TV, the X-Card would be my reccomendation.
Gary
