is = {};
is.agent = navigator.userAgent.toLowerCase();

is.ie4  = (is.agent.indexOf("msie 4")   != -1);
is.ie5  = (is.agent.indexOf("msie 5")   != -1);
is.ie55 = (is.agent.indexOf("msie 5.5") != -1);
is.ie6  = (is.agent.indexOf("msie 6")   != -1);
is.ie7  = (is.agent.indexOf("msie 7")   != -1);
is.ie8  = (is.agent.indexOf("msie 8")	!= -1);	
is.ie   = (is.ie4 || is.ie5 || is.ie55 || is.ie6 || is.ie7 || is.ie8);

is.ns4  = (is.agent.indexOf("4") != -1 && document.layers);
is.ns6  = (is.agent.indexOf("netscape6") != -1);
is.ns7  = (is.agent.indexOf("netscape7") != -1);
is.ns   = (is.ns4 || is.ns6 || is.ns7);

is.moz  = (is.agent.indexOf("gecko") != -1);
is.mac  = (is.agent.indexOf("mac")   != -1);
is.win  = (is.agent.indexOf("win")   != -1);

is.dom  = (is.ie5 || is.ie55 || is.ie6 || is.ie7 || is.ie8 || is.ns6 || is.ns7 || is.moz);