Сократил на солько можно без тестирования.))
<script type="text/javascript">
var today = new Date();
var yearday = Math.ceil((+today - today.setMonth(0,0)) / 864e5);
today.setMonth(12,366);
var leap = today.getDate()!=1?'leap':'';
var d = 'yenonotie_files/';
var id = function(i){return document.getElementById(i)};
if (yearday > 360)
{
id("pic1").src = d+'main/enderi'+leap+'.png';
id("pic2").src = d+'enderi/' + (yearday+(yearday==365&&leap)) + '.png';
}
else
{
id("pic1").src = d+'main/calendar.png';
id("pic2").src = d+'months/' + Math.floor(yearday/30) + '.png'; //возможно (Math.floor(yearday/30)+1)
id("pic3").src = d+'days/' + yearday%30 + '.png';
}
</script>
Переименовать ->
yenonotie_files/enderi/1.png yenonotie_files/enderi/361.png
yenonotie_files/enderi/2.png yenonotie_files/enderi/362.png
yenonotie_files/enderi/3.png yenonotie_files/enderi/363.png
yenonotie_files/enderi/4.png yenonotie_files/enderi/364.png
yenonotie_files/enderi/5a.png yenonotie_files/enderi/365.png
yenonotie_files/enderi/5b.png yenonotie_files/enderi/365leap.png
yenonotie_files/enderi/6.png yenonotie_files/enderi/366.png
yenonotie_files/main/enderi5.png yenonotie_files/main/enderi.png
yenonotie_files/main/enderi6.png yenonotie_files/main/enderileap.png