var bb_on=new Image()
 bb_on.src="Images\\back_btn_off.gif"
 var bb_off=new Image()
 bb_off.src="Images\\back_btn_on.gif"
 var fb_on=new Image()
 fb_on.src="Images\\fwd_btn_off.gif"
 var fb_off=new Image()
 fb_off.src="Images\\fwd_btn_on.gif"