Here is a quick example of my results so far...
http://www.youtube.com/watch?v=Sa04GhS99pw
Edit: There are a few more there now.
Really this is a 312.5 line 50 fps progressive scan signal rather than 625 25 fps interlaced scan - but in terms of bandwidth and the display it's the same thing, at least in regards to line count and frame rate - you will understand that the horizontal resolution is necessarily limited.
This approach, albeit using PICs, is relatively popular method on the internet these days, but why buy PICs when you have half a dozen old P4s lying about the place

In truth I have discovered I can do the same thing, probably better, using the $4.50 Launchpad modules I referred to elsewhere on this forum, but I have always wanted to try it this way...