Variable width nav links?

[shadowkitty]

I'm trying to make my layout of variable width, but I'm stuck on the nav links.

This is how they look at the width where I've managed to get them right:



But this is how they look at another:



This is what the CSS looks like at the moment:

ul.nav {
width: 820px;
margin: 0px auto;
padding: 10px 0px 80px 0px;
list-style-type: none;
font-size: 14px;
letter-spacing: 0.1em;}

ul.nav li {
margin-left: 640px;}

Thanks for any help you might be able to give.