Here you can find a working example, with some more suggestions about dynamic resizing of the list.
I've used display:inline-block and a percentage padding so that the parent list can dynamically change size:
display:inline-block;
padding:10px 1%;
width: 30%
plus two more rules to remove padding for the first and last items.
ul#menuItems li:first-child{padding-left:0;}
ul#menuItems li:last-child{padding-right:0;}