DIV层显示登录窗口 模拟ajax窗口

function ScreenConvert()
{
var browser = new Browser1();
var objScreen = document.getElementById("ScreenOver");
if(!objScreen)
var objScreen = document.createElement("div");
var oS = objScreen.style;
objScreen.id = "ScreenOver";
oS.display = "block";
oS.top = oS.left = oS.margin = oS.padding = "0px";
if (document.body.clientHeight) {
var wh = document.body.clientHeight + "px";
}else if (window.innerHeight){
var wh = window.innerHeight + "px";
}else{
var wh = document.body.scrollHeight;
}

oS.width = "100%";
oS.height = wh;
oS.position = "absolute";
oS.zIndex = "3";
if ((!browser.isSF) && (!browser.isOP)){
oS.background = "#555";
}else{
oS.background = "#555";
}
oS.filter = "alpha(opacity=65)";
oS.opacity = 60/100;
oS.MozOpacity = 60/100;
document.body.appendChild(objScreen);
var allselect = document.getElementsByTagName("select");
for (var i=0; i<allselect.length; i++)
allselect[i].style.visibility = "hidden";
}
function Browser1(){

var ua, s, i;
this.isIE = false;
this.isNS = false;
this.isOP = false;
this.isSF = false;
this.isFF = false;
ua = navigator.userAgent.toLowerCase();
s = "opera";
if ((i = ua.indexOf(s)) >= 0){
this.isOP = true;return;
}
s = "msie";
if ((i = ua.indexOf(s)) >= 0) {
this.isIE = true;
return;
}
s = "netscape6/";
if ((i = ua.indexOf(s)) >= 0) {
this.isNS = true;
return;
}
s = "gecko";
if ((i = ua.indexOf(s)) >= 0) {
this.isNS = true;
return;
}
s = "safari";
if ((i = ua.indexOf(s)) >= 0) {
this.isSF = true;
return;
}

s = "Firefox";