Ajax-Tools /Auto Completer ...

I don't seem to get this combination working :?
I installed the dependency for Auto Completer, Ajax(tools). Now I made a Module that holds the Auto Completer and put it in the right column in the layout. So now it's nicely showing on the site. But it still doesn't do much 'cause I got stuck in the part where to put the necessary changes.
For instance: Where can I find "Mootools Request-Class as an url" and do I have to change something in the code or just plunge something somewhere in the backend ?
Couldn't find any help on this topic, Guess it's all clear to everybody and lot's of people can help me :D
Thnx! GreetZzz Atti