Change image on date

[btb]

Hi

I have a header image on my site, but have 3 different styles - 1 for xmas, 1 for easter and another one to display at other times of the year!
What i'm wanting to know without having to either rename the header image file and upload or change the css file for those 3 times of the year, can css do this by itself at all?

Here is the code in the css:
#header {
background-image: url('site-header.jpg');
width: 800px;
height: 100px;
}

and here is the code in the php/html page:
<div id="header"></div>

and by going to enthusiasts guide to Brisbane Transport, you'll see what i mean, and for the header images, they are:
http://btbuses.info/site-header%20XMAS.jpg
http://btbuses.info/site-header%20EASTER.jpg
http://btbuses.info/site-header.jpg

Your suggestions are most welcomed. Thankyou...

[ALL]

what you could do is use javascript...

something like:

document.onload = function (){
  var header = document.getElementById('header');
  var January = 0;var Febuary = 1;var March = 2;var April = 3;var May = 4;var June = 5;var July = 6;var August = 7;var September = 8;var October = 9;var November = 10;var December = 11;
  var date = new Date();
  if(date.getMonth() == March && date.getDate() > 1 && date.getDate() < 15){
    header.id = 'header_easter';
  }else if(date.getMonth() == December && date.getDate() > 1 && date.getDate() < 31){
    header.id = 'header_christmass';
  }
}

try something like that in your head, then in your css make an id called 'header_christmass' and 'header_easter' with the new background image in it, and it will change based on the user's internal computer's time.