Step 1 on a mission to sort out browser differences in ordered (ol) and unordered (ul) lists, when links (a href) are used and with IE's whitespace issues. For the fully worked version see AmR's wordpress tab menu navigation widget.
This plain version works in Firefox 2 and IE6 and 7 on windows vista, and possibly others. Unfortunately we still have a form of the whitespace bug, which is really only an issue if you want the elements to be snug up next to each other. Some fixes for horizontal menu's are here. Yes messing around with having and not havng spaces does sort them out, but is this good enough for a widget solution? I suspet that the safest option may be to produce "tight" code.
Image showing horizontal lists in IE7
Image showing horizontal lists in Firefox
