使用jQuery Ajax自动完成？

Right now I am populating a dropdown div of an input with data on an unordered list on afterauth.php with this code (on keyup of the input):

$("#dropdown").load("../invites/afterauth.php");

All this code does is when i type into the input, it loads the data in a nice list in the dropdown div.

I need to be able to do a bit more:

First, I want the data that drops down to act as an "autocomplete" for the characters being entered in the input. So if I begin typing "ac" into the input, data from afterauth.php such as "actual" and accept" will show in the dropdown.

Second, I want to limit the data shown on the dropdown list to 6 items, and again, I'm confused on how to do that.

Thanks!

$("#dropdown").autocomplete('../invites/afterauth.php',{key:value});

key and value pair should be as per ajax call.