The jQuery library, and virtually all of its plugins are constrained within the jQuery namespace. As a general rule, “global” objects are stored inside the jQuery namespace as well, so you shouldn’t get a clash between jQuery and any other library (like Prototype, MooTools, or YUI).

That said, there is one caveat: By default, jQuery uses “$” as a shortcut for “jQuery”‘

Credit : http://docs.jquery.com/Using_jQuery_with_Other_Libraries