isDOM = document.getElementById //DOM1 browser (MSIE 5+, Netscape 6, Opera 5+)
isOpera = isOpera5=window.opera && isDOM //Opera 5+
isOpera6 = isOpera && window.print //Opera 6+
isOpera7 = isOpera && document.readyState //Opera 7+
isMSIE = document.all && document.all.item && !isOpera //Microsoft Internet Explorer 4+
isMSIE5 = isDOM && isMSIE //MSIE 5+
isNetscape4 = document.layers //Netscape 4.*
isMozilla = isDOM && navigator.appName=="Netscape" //Mozilla или Netscape 6.*
// Kruglov S. A. (kruglov.ru)