It depends on exactly what dynamics you need.
You obviously can't have a site that fits all windows without scaling all the elements and that would be silly anyway.
If you just want a background that fills the viewport height then you are probably looking at a sticky footer effect. You can read up on it in the CSS faq (see link in my sig - there is also a faq on 100% height you may find useful).
If on the other hand you want a header and footer always fixed to the top and bottom of the viewport then you are looking at fixed positioning which is something different again.
We'd need to see a picture of your design and what you would expect to happen to the layout at various sizes.
Suffice to say that usually doing none of the above is the best approach and content should dictate what the page looks like Just let it flow and adjust to screen sizes automatically. Everyone expects to scroll vertically so there is no need to avoid this.