Actualy AJAX is new becuase it involves a new process (retrieving data from the server after the page has finished loading.
Well to be fair the XMLHttpRequest API (or rather its MS equivalent) has been available for about five years in IE and there were methods of doing similar things before that using tricks with frames and stuff. The API became available in Mozilla in 2002. I can't quite put my finger on when AJAX was first coined, but it was quite recently and the use of this raft of technologies certainly predated the naming.
Update: The Wikipedia article on Ajax clearly indicates how far the use of these technologies predates the coining of the name.