Create form without JavaScript
No, not really. JavaScript is the only way to have content (including forms) change on a page without relaod. Now you have two ways to go around it:


Make all choices available in all 3 downloads and only hide unneeded ones using JavaScript. That way if someone will not have JS enabled, he will see all choices and will be able to make his selection. Don't forget to test if his selection is sane on the server side!
Use multi-step form. See this question and accepted answer. That way you will be able to ask one thing at a time, serving new steps using good old HTTP.