if (document.images)
{
     ImageOver = new Array(16);                
     ImageOut = new Array(16);
     
     for(var i=1; i<=5; i++)
     {
          ImageOver[i] = new Image;
          ImageOut[i] = new Image;
          
          ImageOver[i].src ="images/bt"+i+"_over.gif";
          ImageOut[i].src ="images/bt"+i+".gif";
     }
}

function ImgOver(i)
{
     if (document.images)
     {  
     document.images["pic" + i].src = ImageOver[i].src;  
     }   
}

function ImgOut(i)
{
     if (document.images)
     { 
     document.images["pic" + i].src = ImageOut[i].src;  
     }
}