The problems were not apparent from install but seem to have crept into MCE over the last day or so. On top of the MCE install, I have also installed a couple of plugins, which again as with MCE, have been fine and running well.
The thing that worries me is that Windows 7 installed a graphics card driver
update yesterday and it was a pre-release update (a little naughty Windows 7 suggesting a beta release I thought) but I installed it any way. I suspect this may have something to do with the problems; which, coincidently manifested themselves yesterday! Will back this out and see how I go.
BTW - I am using a terratec cinergy 2400i dt card, picture is c.clear.