var now = new Date();
now.setTime(now.getTime() - 0);
var day = now.getDay();
var date = now.getDate();
var month = now.getMonth();
var year = now.getFullYear();
year += (year < 1900) ? 1900 : 0;

var months = new Array();
 months[0] = "jan";
 months[1] = "feb";
 months[2] = "mar";
 months[3] = "apr";
 months[4] = "may";
 months[5] = "jun";
 months[6] = "jul";
 months[7] = "aug";
 months[8] = "sep";
 months[9] = "oct";
months[10] = "nov";
months[11] = "dec";

document.write('<link rel="stylesheet" type="text/css" href="css/main_' + months[month] + '.css" />');

delete now;