@mellonm, you can with the custom design upgrade using CSS, but there as with every rose, there are thorns and the biggest two thorns are:
1. All browsers render things differently. On one browser your menu many be nicely spaces and take up the entire area and the next browser may render differently and show the menu in two lines, pushing the last item down.
2. You cannot control the settings people make to their own browsers. They can change the minimum font size to render sites in (which will muck you up) or they can use the browser zoom feature (which will muck you up).
The web just isn't really entirely controllable. Too many things outside your control.