Make navigation fit 100% of the nav bar

I’m having a bit of trouble figuring this one out.

I’m trying to make it so my unordered menu list expands to the whole width of my navigation bar. Much like how you would make a table so it takes up the whole navigation bar. However, as i’m using wordpress 3 custom menu i’m not sure how to achieve the same effect.

If you look at the image you’ll notice the “About us” menu item doesn’t extend to the end – does anyone know of any css that I can use to achieve the same effect a table would offer?

http://temp.55uk.net/nav_flaw.jpg

Many thanks for looking 🙂