Dropdown / Forms

i need to be able to select the year and according to the year only be able to select certin months.

i was thinking an if statement but (if year = 2006 then months= jan,mar,dec) sorta thing but i cant get that part working. any direction would be nice.

maybe there's an easier/different way to do this?

<script language="javascript">

function downloadForm(formMonth,formYear){
month = document.getElementById(formMonth).value;
year= document.getElementById(formYear).value;
location.href = "/pdf/qa/customer-satisfaction-leaderboards-" + year + "-" + month +".pdf";
}</script> Code: