function Browser() {
  var ua, s, i;
  this.isIE = false;
  this.isNS = false;
  this.isMozilla = false;
  this.version = null;
  ua = navigator.userAgent;
  s = "MSIE";
  if ((i = ua.indexOf(s)) >= 0) {
    this.isIE = true;
    this.version = parseFloat(ua.substr(i + s.length));
    return;
  }

  s = "Netscape/";
  if ((i = ua.indexOf(s)) >= 0) {
    this.isNS = true;   
    this.version = parseFloat(ua.substr(i + s.length));
    return;
  }
  s = "Netscape6/";
  if ((i = ua.indexOf(s)) >= 0) {
    this.isNS = true;   
    this.version = parseFloat(ua.substr(i + s.length));
    return;
  }
  s = "Mozilla/";
  if ((i = ua.indexOf(s)) >= 0) {
    this.isMozilla = true;   
    this.version = parseFloat(ua.substr(i + s.length));
    return;
  }
  
}

var browser = new Browser();

function checkBrowser() {
  var ok=false
  if(browser.isIE && browser.version >= 5.01) ok=true;
  if(browser.isNS && browser.version >= 6) ok=true;
  if(browser.isMozilla && browser.version >= 5) ok=true;
  return ok   
}