If you plan not to reuse and existing AJAX component here are some of the things you will need to know.
Plan to learn Dynamic HTML (DHTML),
* DOM -
An API for accessing and manipulating structured documents. In most cases DOM represent the structure of XML and HTML documents.
* CSS -
Understanding the basic request/response nature of HTTP is also important. Many subtle bugs can result if you ignore the differences between the GET and OIst methods when configuring an XMLHttpRequest
and HTTP response codes when processing callbacks.