Very many thanks to those of you that replied.
I have obtained a copy of WinDVR 3 (legally) and having installed that on my other machine (Athlon 2.2/other items as previous except Jetway mobo) I seem to have resolved my problem.

I was sure the Pinnacle software was the problem - WinDVR 3 is faultless on this slightly lower spec machine so I reckon it will be more than OK on the P4 described in my original question.

Only thing is that the teletext function in WinDVR 3 dosent work - thought that a bit strange as the Pinnacle cards obviously have the decoder built in as they supply their PC Teletext software which isnt too bad at what it does - perhaps the WinDVR 3 software dosnt work with the Pinnacle decoder, oh well you cant win them all !! - still I can use the Pinnacle software for teletext viewing - anyone care to comment on this teletext not work matter.

All I can say is from initial tests and the results I would reccomend WinDVR 3 without reservation - would be very interested to hear your comments and thoughts on WinDVR 3.

Once again, a big thankyou to you all.