It seemed that the only way to do this was with absolute positioning, which I wanted to avoid if at all possible!
Then I came across this article by Shaun Inman and my problem was solved! He describes the solution much better than I can so I advise you to go have a look see if such things make you moist.
He has a really simple CSS and JS resolution to the problem so I copied it down and into a NSF page to see if it would work and it does!! Wonderfully fluid centered [div]s with a header at the top and a footer at the bottom ..(see below) ... Yippee ... Just what I wanted. Now if I can just get it to work in xPages which is being somewhat of a puzzle, but I shall continue on regardless. More tomorrow.