full width main menu

Hello. I'm trying to set my main menu to stretch the entire width of the mainmenu container, but I'm not having much luck with the css. I've seen posts that reference centering the menu items, but in addition to centering, I would like then to use the entire width of the container. An example of the current menu can be seen at: www.lisaboslett.com/mainmenu.png The menu items are left justified. What css would I use to center them across the entire width of the container (978px)? Any help would be greatly appreciated.