Here's another tip if we are posting them:
A flash movie supports % height/width.
If you have a 3 column layout, or whatever, and want the center column header to stretch, put a flash movie in there, and set it to 100% width. When the browser is resized, it will shrink/grow with the page, instead of dawning the dreaded horizontal scrollbar.
Just thought I'd post this. Not sure if anyone has used this yet, but, I've tested it in IE and NS4.