if(window.navigator.userAgent.indexOf("MSIE") > -1)
{
  width = screen.availWidth;
}
else
{
  width = innerWidth;
}

if (width > 640)
{
  document.writeln("<link rel=\"stylesheet\" type=\"text/css\" href=\"css/standard.css\">");
}
else if (width > 1024)
{
  document.writeln("<link rel=\"stylesheet\" type=\"text/css\" href=\"css/standard_big.css\">");
}