function roll_over(img_name, img_src)
{
    var img = document.getElementById(img_name);
    img.src = img_src;
}

function preloadImages()
{
     // set image list
     imageList = new Array(
        '_img/interior/nav_resources.gif',
        '_img/interior/nav_resources_highlight.gif',
        '_img/interior/nav_resources_on.gif',
        '_img/interior/nav_seminars.gif',
        '_img/interior/nav_seminars_highlight.gif',
        '_img/interior/nav_seminars_on.gif',
        '_img/interior/nav_consulting.gif',
        '_img/interior/nav_consulting_highlight.gif',
        '_img/interior/nav_consulting_on.gif',
        '_img/interior/topnav_1.gif',
        '_img/interior/topnav_1_off.gif',
        '_img/interior/topnav_2.gif',
        '_img/interior/topnav_2_off.gif',
        '_img/interior/topnav_3.gif',
        '_img/interior/topnav_3_off.gif',
        '_img/interior/topnav_4.gif',
        '_img/interior/topnav_4_off.gif',
        '_img/interior/topnav_5.gif',
        '_img/interior/topnav_5_off.gif',
        '_img/interior/topnav_6.gif',
        '_img/interior/topnav_6_off.gif');
        
     images = new Array();

     // start preloading
     for(i = 0; i <= imageList.length; i++)
     {
          document.writeln('<img style="display:none;" src="' + imageList[i] + '"/>');
     }
}

preloadImages();