http://www.onderdelenzoeker.nl/
On this website when you select a year it shows a few more fields to choose from and the options are filtered for just that year without refreshing the page or anything.
I cannot figure out how to do this, can someone help me out?
You just have to hook into the change event, and load the other options there. If you have to load those other options dynamically, you'll have to make an AJAX request.
Check out this video tutorial, which explains exactly how to do this:
Remy Sharp: Populate Select Boxes.