Thought I'd update on my purchases:
£180 Lenovo Q180, ebuyer
£55 PCTV 290e USB dual DVB-t USB stick, and USB DVD drive. PC world
£30 samsung se 208ab tsbs external slimline DVD writer
Total cost £265
Installed mythbuntu, TV tuner just worked, sound for live TV and recordings no problem. Still haven't got sound working in mythbunutu dvd plyer, but works in VLC.
HDTV not working unfortunately. I assume that this is a driver issue as the ATI 6xxxx series graphics card should handle it no problem. Tried the AMD drivers rather than the ones in the repository but to no avail.
PC fan could be quieter, but you don't notice when the TV is on.
Still to get a wireless keyboard and mouse.
Using my android phone for the remote.