Ease your headache with these Javascript library.
Aren’t they cool or what!
Prototype HomePage
Here is the well explained how-to-use guide
http://24ways.org/advent/easy-ajax-with-prototype
moo.fx : AJAX library
Some nice effect can be implemented without hassle.
http://script.aculo.us/
http://wiki.script.aculo.us/scriptaculous/show/CombinationEffectsDemo