just thought I'd update this myself, in case anyone else has the same problem: this worked:
http://www.salloway.org.uk/mediacenter/util/
when I re-ran the setup it all worked fine. I wish I'd found this before:
re-installing the video drivers (several times), installing windows genuine advantage (2 versions as the first one didn't work) to get the video decoder checker utility, which showed I needed a new video decoder, reinstalling windvd, running another repair tool I found via this blog post:
http://blogs.msdn.com/astebner/archi...20/483215.aspx, as well as many joyless hours spent online searching for answers. IT would've been cheaper to go out and buy a hardisk recorder.

Ok moan over