got it, figured it out :).

On the preview window,make sure the project properties are the same as the project footage.
Then go through the variuos settings for preview,ie "Draft!,"good" "best" etc,try them all on "full","quarter","half" etc.

For your info,my small preview window is perfect,but when i view in full screen on my 2nd monitor,both windows loose the smoothness a bit.This is on a quad core pc with 4gb ram,graphics card with it's own 256 ram.

If i thought i could make both windows/monitors smooth by uprating my graphics card,i would,but no-ones gave me any advice on this.

Paul.

Thank you Paul for the advise, I guess you were typing it while I was viewing one of the other threads which gave me the answer to it. Next time will make better use of the search option :).