A method to distribute elements evenly in a container using CSS appeared on Smashing Magazine today.
I recently had to use Javascript to achieve the same effect for
This is what display:table-cell is supposed to achieve - however, the IE's just don't do it, and FF<3 has problems with it too, I believe.
These styles work in FF3, Chrome, Safari, and (I think) Opera 9:
#menu ul {display:table;padding:0;}
#menu li {display:table-cell;text-align:center;}
But you'll need a fair few hacks to get them working in the usual, commercial set of browsers.