var navbutton_off  = new Image();
var navbutton_roll  = new Image();

navbutton_off.src  = 'http://www.securitycentralinc.com.cnchost.com/images/navbutton_off.gif';
navbutton_roll.src  = 'http://www.securitycentralinc.com.cnchost.com/images/navbutton_roll.gif';