// JavaScript Document
if (document.images) {

  image1on = new Image();
  image1on.src = "images/port/enkin_over.gif";

  image2on = new Image();
  image2on.src = "images/port/rg_over.gif";

  image3on = new Image();
  image3on.src = "images/port/tapline_over.gif";

  image4on = new Image();
  image4on.src = "images/port/senensky_over.gif";

  image5on = new Image();
  image5on.src = "images/port/kari_over.gif";

  image6on = new Image();
  image6on.src = "images/port/cedholl_over.gif";
  
  image7on = new Image();
  image7on.src = "images/port/enkinprint_over.gif";
  
  image8on = new Image();
  image8on.src = "images/port/pilatesroom_over.gif";
  
  image9on = new Image();
  image9on.src = "images/port/kas_over.gif";
  
  image10on = new Image();
  image10on.src = "images/port/rgprint_over.gif";
    
  image11on = new Image();
  image11on.src = "images/port/bouchercon_over.gif";
  
  image12on = new Image();
  image12on.src = "images/port/krprint_over.gif";
  
  image1off = new Image();
  image1off.src = "images/port/enkin.gif";

  image2off = new Image();
  image2off.src = "images/port/rg.gif";

  image3off = new Image();
  image3off.src = "images/port/tapline.gif";

  image4off = new Image();
  image4off.src = "images/port/senensky.gif";

  image5off = new Image();
  image5off.src = "images/port/kari.gif";

  image6off = new Image();
  image6off.src = "images/port/cedholl.gif";
  
  image7off = new Image();
  image7off.src = "images/port/enkinprint.gif";
  
  image8off = new Image();
  image8off.src = "images/port/pilatesroom.gif";
  
  image9off = new Image();
  image9off.src = "images/port/kas.gif";
  
  image10off = new Image();
  image10off.src = "images/port/rgprint.gif";
    
  image11off = new Image();
  image11off.src = "images/port/bouchercon.gif";
  
  image12off = new Image();
  image12off.src = "images/port/krprint.gif";
 
}

function changeImages() {
  if (document.images) {
    for (var i=0; i<changeImages.arguments.length; i+=2) {
      document[changeImages.arguments[i]].src = eval(changeImages.arguments[i+1] + ".src");
    }
  }
}

<!-- preload images

function MM_preloadImages() { //v3.0
  var d=document; if(d.images){ if(!d.MM_p) d.MM_p=new Array();
    var i,j=d.MM_p.length,a=MM_preloadImages.arguments; for(i=0; i<a.length; i++)
    if (a[i].indexOf("#")!=0){ d.MM_p[j]=new Image; d.MM_p[j++].src=a[i];}}
}
//-->