When you can use jQuery?
You should use jQuery when you need:
* A small library that gives you powerful control over the Document Object Model
* With very little effort or work on your part
* Quick access to AJAX
* Without a lot of bloat (overhead - wasted code)
* And some basic animation effects to spice things up
If you need super fancy effects for animation, drag and drop, and super smooth animation then you will probably want to use Prototype and one of the many great library created to enhance the effects.