function TwoStateRollOver(label,inactive,active,status) {
      this._canRoll   = _canThisBrowserHandleImageRolls();
      this._imageId   = label;
      this._winStatus = status;
      this.isActive   = false;
      if( this._canRoll ) {
         this.activeImg         = new Image();
         this.activeImg.src     = active;
         this.inactiveImg       = new Image();
         this.inactiveImg.src   = inactive;
      }
      this.mouseOver = _rollActive;
      this.mouseOut  = _rollInactive;
   }
   function _rollActive(){
      if ( this._canRoll && !this.isSelected ){
         document.images[this._imageId].src = this.activeImg.src;
      }
      this.isActive = true
      window.status = this._winStatus;
   }
   function _rollInactive(){
      if ( this._canRoll ){
         if( !this.isSelected ) {document.images[this._imageId].src = this.inactiveImg.src;}
      }
      this.isActive = false
      window.status = '';
   }
   function _canThisBrowserHandleImageRolls() {
      if (navigator.appName == "Microsoft Internet Explorer") {
         if(parseInt(navigator.appVersion) >= 4) {
            return( 1 );
         } else {
            return( 0 );
         }
      } else if (navigator.appName == "Netscape") {
         if(parseInt(navigator.appVersion) >= 3) {
            return( 1 );
         } else {
            return( 0 );
         }
      }
   }

/*
//example instantiation
preshow_roll= new TwoStateRollOver( "preshow", <-- image name
                     "images/rollovers/preshow_off.gif", <-- state one
                     "images/rollovers/preshow_on.gif",  <-- state two
                     "Alt Tag");
*/