function resizeMenu($navItem, menuWidth){
    var sizeConcat = 0
    $navItem.each(function(e){
        sizeConcat += $(this).width()    
    })

    var widthDif = ((menuWidth-(sizeConcat))/$navItem.length-1)

    $navItem.each(function(e){
       var itemWidth = Math.round(widthDif + $(this).width()) 
       $(this).css({'width': itemWidth +'px'});
    })
}

http://jsfiddle.net/bra4C/

This is a little function that dynamically resizes the navigation, taking into account the size of the item width as well

Dynamic Menu Resizer

css, navigation, jquery

jQuery