it's mostly a matter of using 'table width=100%' or something close to 100% depending on your design. The key is that you can't just go and do it (usually) it's something that has to be considered from the start of the design since it will affect how the images are created and sized etc.
the other factor to take into account is how the site will "flex" as the display changes...this means building sections of a page that maintain a geometric relationship whilst shifting around the page to fill the space
"liquid" is a good word to use...I tend to use kinetic though...it implies a much less chaotic system
I've worked with making the site here more liquid and I think some of the minor things worked out good. 'course, I'm in the position of not being chained to heavy graphics and am fortunate to have a fairly static layout. I love the "page size" option in Opera where you can see the pixel size in the title bar - just move it around to check the various sizes.