You'll need some Javascript - otherwise you'll have nothing to go in the dropdown's onChange() handler! Without that handler, there'll be nothing to tell anything to update the second dropdown when the first changes.
That said, it's still possible to update the second dropdown by requesting a new version from the server; I outlined an approach in this thread. Notice that (as I said), some Javascript is still needed.
The advantage of doing the dropdown refresh on the server is that you don't need to download every possible content for the second drop down with every request for the page; the disadvantage is that updating the second dropown is a lot slower.
