loaded = false;

function preLoad()
{
  iPath= 'images/';  iExt= 'png';
  var suffix= new Array ('-on', '-off');

  if(document.images)
  {
    var argLen = arguments.length;
    for(var i = 0; i < argLen; i++)
    {
      var arg = arguments[i];
      var sufLen = suffix.length;

      for (j = 0; j < sufLen; j++)
      {
        var suf = suffix[j];
        self[arg + suf] = new Image();
        self[arg + suf].src = iPath + arg + suf + '.' + iExt;
      }
    }
    loaded = true;
  }
}

function rollOver(iName, iState)
{
  if(document.images && loaded)
  {    
    document.images[iName].src = self[iName + '-' + iState].src;
  }
}