Depends on what you need, you might use Html control
with Javascript in your web part to achieve the
purpose without touching AJAX.

The basic idea is that the CreateChildControl() method
create all Html controls with embedded logic in the
JavaScript functions (onclick, onchange etc.). The
CreateChildControl() method also loads server  side
information to be used in Html controls and JavaScript
functions. But once that is done, everything else is
controlled by the JavaScript which runs on the client
side.

The code can look very ugly.

And it won't work if client needs to interact with
server later because it is hard (impossible without
AJAX?) to get value from an Html control to a web
control. I believe AJAX will come in handy. I hope
someone else will share her/his experience.