function lib_bwcheck(){  
    this.ver=navigator.appVersion 
    this.agent=navigator.userAgent 
    this.dom=document.getElementById?1:0 
    this.opera5=this.agent.indexOf("Opera 5")>-1 
    this.ie5=(this.ver.indexOf("MSIE 5")>-1 && this.dom && !this.opera5)?1:0;  
    this.ie6=(this.ver.indexOf("MSIE 6")>-1 && this.dom && !this.opera5)?1:0; 
    this.ie7=(this.ver.indexOf("MSIE 7")>-1 && this.dom && !this.opera5)?1:0; 
    this.ie4=(document.all && !this.dom && !this.opera5)?1:0; 
    this.ie=this.ie4||this.ie5||this.ie6||this.ie7 
    this.mac=this.agent.indexOf("Mac")>-1 
    this.ns6=(this.dom && parseInt(this.ver) >= 5) ?1:0;  
    this.ns4=(document.layers && !this.dom)?1:0; 
    this.firefox = this.agent.indexOf("Firefox")>-1 
    this.bw=(this.ie7 || this.ie6 || this.ie5 || this.ie4 || this.ns4 || this.ns6 || this.opera5 || this.firefox) 
    return this 
} 
var bw=new lib_bwcheck()