var agt=navigator.userAgent.toLowerCase();
var is_major = parseInt(navigator.appVersion);
var is_minor = parseFloat(navigator.appVersion);
var is_gecko = (agt.indexOf('gecko') != -1);
var is_ie    = ((agt.indexOf("msie") != -1) && (agt.indexOf("opera") == -1));
var is_ie3   = (is_ie && (is_major < 4));
var is_ie4   = (is_ie && (is_major == 4) && (agt.indexOf("msie 4")!=-1) );
var is_ie5up = (is_ie && !is_ie3 && !is_ie4);
if (is_ie5up || is_gecko) {
}