CSS question

OK, so I have a site I customized in flash (the base is ZipCSS a little guide thing for CSS), and it’s working pretty well, but when it is maximized, the main bit of the site (where all the text is) does not reach to the bottom, which I want it to do.

I could add a bunch of <br>s but then there would be blank space at the bottom, which I really don’t want.

Is there a way to make it as long as the browser window is?