Hi ML - There are 2 ways I know of to do this. One is to float everything. Then it all rearranges itself to fit the window. Everything is always onscreen, but it's not always pretty.
Another is to code the widths of divs and images etc, in percents. I believe there are some issues with fonts in percents and maybe others, but in general it works very well. You can make every 'box' or container shrink or expand, and images too. The text (in ems or pixels) will flow and push down the bottom of their containers.
I've been using this method very successfully. I did get one big surprise though. Coding on a 1024x368 screen, I discovered that many of my web optimized images became very grainy and filled with artifacts and moire patterns when viewed on a computer with a 1200x800 screen. But hey, the tweaking never stops :).
Many here know alot more than I do about CSS,and they may have something to say on issues with IE and other things when using percents.
[edited by: commanderW at 11:59 pm (utc) on Dec. 2, 2008]