Uses the Zend Framework but it can be done without, Just code no examples at this time will get that up shortly plus some basic help.

http://www.cyberlot.net/demos/auto_xajax_jquery/

The basic files, I haven't had time to pull together any real docs/working examples but the code is pretty clear.

Setting up an autocomplete is as simple as doing

$("#ac_me").xg_autocomplete() at the bottom of a page

Some other neat little tricks included, Injecting a ZF view into an element.