function isValidBrowser()
{
var result = 'ns';
if ( navigator.appVersion.indexOf('MSIE 6.') != -1) { result = 'ie6' }
if ( navigator.appVersion.indexOf('MSIE 5.') != -1) { result = 'ie5' }
if ( navigator.appVersion.indexOf('MSIE 4.') != -1) { result = 'ie4' }
return result
}