document.onkeydown = NavigateThrough;  
function NavigateThrough (event) {  
     if (!document.getElementById)  
         return;  
     if (window.event)  
         event = window.event;  
     if (event.ctrlKey) {   
         var link = null;   
         var href = null;   
         switch (event.keyCode ? event.keyCode : event.which ? event.which : null) {  
             case 0x25: link = document.getElementById ('previous_page'); break;   
             case 0x27: link = document.getElementById ('next_page'); break;   
             case 0x26: link = document.getElementById ('up_page'); break;   
             case 0x28: link = document.getElementById ('down_page'); break;   
             case 0x24: link = document.getElementById ('home_page'); break;   
         }   
           
         if (link)   
             document.location = link.href;   
         }   
 }