function showCalendar(str_target, str_datetime) {
	var arr_months = ["January", "February", "March", "April", "May", "June",
		"July", "August", "September", "October", "November", "December"];
	var week_days = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
	var n_weekstart = 0; // day week starts from (normally 0 or 1)
	
	var dt_datetime = (str_datetime == null || str_datetime =="" ?  new Date() : str2dt4(str_datetime));
	var dt_prev_month = new Date(dt_datetime);
	dt_prev_month.setMonth(dt_datetime.getMonth()-1);
	if (dt_datetime.getMonth()%12 != (dt_prev_month.getMonth()+1)%12) {
		dt_prev_month.setMonth(dt_datetime.getMonth());
		dt_prev_month.setDate(0);
	}
	var dt_next_month = new Date(dt_datetime);
	dt_next_month.setMonth(dt_datetime.getMonth()+1);
	if ((dt_datetime.getMonth() + 1)%12 != dt_next_month.getMonth()%12)
		dt_next_month.setDate(0);
	
	var dt_firstday = new Date(dt_datetime);
	dt_firstday.setDate(1);
	dt_firstday.setDate(1-(7+dt_firstday.getDay()-n_weekstart)%7);
	var dt_lastday = new Date(dt_next_month);
	dt_lastday.setDate(0);
	
	// html generation (feel free to tune it for your particular application)
	// print calendar header
	var str_buffer = new String (
		"<HTML>"+
		"<HEAD>"+
		"	<TITLE>Softrim [calendar]</TITLE>"+
		"<style>"+
		"a.{color:#AOAOA4;text-decoration:none}"+
		"a:link{color:#AOAOA4;}"+
		"a:active{color:#A0A0A4;}"+
		"a:visited{color:#A0A0A4;}"+
		"a:hover{color:#FFFFFF; text-decoration:none}"+
		"</style>"+
		"<SCRIPT>"+
		"var isIE4 = false;"+
		"function CheckBrowser(){ "+
		"	if (navigator.appName == \"Microsoft Internet Explorer\" && navigator.appVersion.charAt(0) >= 4) { isIE4 = true; }"+
		"}"+
		"function mOvr(src,clrOver){"+
		"	if (!src.contains(event.fromElement)) { src.style.cursor = 'hand'; src.bgColor = clrOver;}"+
		"}"+
		"function mOut(src,clrIn){"+
		"	if (!src.contains(event.toElement)) { src.style.cursor = 'default'; src.bgColor = clrIn;}"+
		"}"+
		"</SCRIPT>"+
		"</HEAD>"+
		"<BODY BGCOLOR=\"#FFFFFF\" TEXT=\"#000000\" TOPMARGIN=3 LEFTMARGIN=3 MARGINWIDTH=3 MARGINHEIGHT=3>"+
			"<TABLE BORDER=0 BGCOLOR=\"#000000\" CELLSPACING=1 CELLPADDING=0 WIDTH=\"100%\" >"+
				"<TR>"+
					"<TD WIDTH=29 BGCOLOR=\"#000066\" HEIGHT=15 style=\"cursor:hand\" onClick=\"javascript:window.opener.showCalendar('"+
				str_target+"', '"+ dt2dtstr4(dt_prev_month)+"');\">"+
						"<P ALIGN=CENTER><a href=\"javascript:window.opener.showCalendar('"+
				str_target+"', '"+ dt2dtstr4(dt_prev_month)+"');\"><FONT COLOR=\"#FFFFFF\" SIZE=\"-2\" FACE=\"Verdana\">«</FONT></P></a>"+
					"</TD>"+
					"<TD COLSPAN=5 BGCOLOR=\"#000066\" style=\"cursor:default\">"+
						"<P ALIGN=CENTER><B><FONT COLOR=\"#FFFFFF\" SIZE=\"-2\" FACE=\"Verdana\">"+arr_months[dt_datetime.getMonth()]+" "+dt_datetime.getFullYear()+"</FONT></B></P>"+
					"</TD>"+
					"<TD WIDTH=28 BGCOLOR=\"#000066\" style=\"cursor:hand\" onClick=\"javascript:window.opener.showCalendar('"
				+str_target+"', '"+dt2dtstr4(dt_next_month)+"');\">"+
						"<P ALIGN=CENTER><a href=\"javascript:window.opener.showCalendar('"
				+str_target+"', '"+dt2dtstr4(dt_next_month)+"');\"><FONT COLOR=\"#FFFFFF\" SIZE=\"-2\" FACE=\"Verdana\">»</FONT></P></a>"+
					"</TD>"+
				"</TR>"+
				"<TR>"
	);

	var dt_current_day = new Date(dt_firstday);
	// print weekdays titles
	//str_buffer += "<tr>\n";
	for (var n=0; n<7; n++)
		str_buffer += "<TD WIDTH=29 BGCOLOR=\"#D2D2D2\" HEIGHT=15 style=\"cursor:default\"><P ALIGN=CENTER><B><FONT SIZE=\"-2\" FACE=\"Verdana\">"+
		week_days[(n_weekstart+n)%7]+"</FONT></B></P></TD>";
	// print calendar table
	//str_buffer += "</tr>\n";
	while (dt_current_day.getMonth() == dt_datetime.getMonth() ||
		dt_current_day.getMonth() == dt_firstday.getMonth()) {
		// print row header
		str_buffer += "<tr>\n";

		for (var n_current_wday=0; n_current_wday<7; n_current_wday++) {
				
				if ((dt_current_day.getMonth() == dt_datetime.getMonth()) && (dt_current_day.getDate() == dt_datetime.getDate()))
					// print current date
					str_buffer += "	<td bgcolor=\"#0099FF\" align=\"right\" HEIGHT=15 onmouseover=\"mOvr(this,'#A6CAF0');\" onmouseout=\"mOut(this,'#0099FF');\" onClick=\"javascript:window.opener."+str_target+
					".value='"+dt2dtstr4(dt_current_day)+"'; window.close();\">";
				else if (dt_current_day.getDay() == 0 || dt_current_day.getDay() == 6)
					// weekend days
					str_buffer += "	<td bgcolor=\"#F0F0F0\" align=\"right\" HEIGHT=15 onmouseover=\"mOvr(this,'#A6CAF0');\" onmouseout=\"mOut(this,'#F0F0F0');\" onClick=\"javascript:window.opener."+str_target+
					".value='"+dt2dtstr4(dt_current_day)+"'; window.close();\">";
				else
					// print working days of current month
					str_buffer += "	<td bgcolor=\"white\" align=\"right\" HEIGHT=15 onmouseover=\"mOvr(this,'#A6CAF0');\" onmouseout=\"mOut(this,'white');\" onClick=\"javascript:window.opener."+str_target+
					".value='"+dt2dtstr4(dt_current_day)+"'; window.close();\">";

				if (dt_current_day.getMonth() == dt_datetime.getMonth())
					// print days of current month
					str_buffer += "<a href=\"javascript:window.opener."+str_target+
					".value='"+dt2dtstr4(dt_current_day)+"'; window.close();\">"+
					"<font color=\"black\" face=\"verdana\" size=\"-2\">";
				else 
					// print days of other months
					str_buffer += "<a href=\"javascript:window.opener."+str_target+
					".value='"+dt2dtstr4(dt_current_day)+"'; window.close();\">"+
					"<font color=\"#A0A0A4\" face=\"verdana\" size=\"-2\">";
				str_buffer += dt_current_day.getDate()+"</font></a></td>\n";
				dt_current_day.setDate(dt_current_day.getDate()+1);
		}
		// print row footer
		str_buffer += "</tr>\n";
	}
	// print calendar footer
	str_buffer +=
		"</table>\n" +
		"</tr>\n</td>\n</table>\n" +
		"</body>\n" +
		"</html>\n";

	var w = 200;
	var h = 135;
	var LeftPosition = (screen.width) ? (screen.width-w)/2 : 0;
	var TopPosition = (screen.height) ? (screen.height-h)/2 : 0;
	var vWinCal = window.open("", "Calendar", 
		"width="+w+",height="+h+",status=no,resizable=no,top="+TopPosition+",left="+LeftPosition);
	vWinCal.opener = self;
	vWinCal.focus();
	var calc_doc = vWinCal.document;
	calc_doc.write (str_buffer);
	calc_doc.close();
}
// datetime parsing and formatting routines. modify them if you wish other datetime format
function str2dt4 (str_datetime) {
	var re_date = /^(\d+)\/(\d+)\/(\d+)$/;
	if (!re_date.exec(str_datetime))
		return alert("Invalid Date format: "+ str_datetime);
	return (new Date (RegExp.$3, RegExp.$1-1, RegExp.$2));
}
function dt2dtstr4 (dt_datetime) {
	return (new String (
			(dt_datetime.getMonth()+1)+"/"+dt_datetime.getDate()+"/"+dt_datetime.getFullYear()));
}