This is really not a good idea as it can really kill frame rates. But if you really want to do one way is to make a separate folder for the aircraft you want to use as AI example if you want to use the default B747-400 make a copy of the B747-400 folder to a temp folder then rename that folder to AIB747-400 then open the folder and remove the panel folder out of it as you do not need it. Once done drag the renamed folder back into your FS aircraft folder. Then all that is left is to assign it to some AI flight plans.
But as I said I strongly recomend that you do not do this as it really does kill your frame rates.
I use projectai they have both fs2000 and fs2004 aircraft and flight plans for everything except for military aircraft and hellicopters.  8)

and wot about frame rate friendly planes?

ok and do i just place them in the aircraft folder?

Put the planes in the aircraft folder and while you do not  need to have AFCAD it might not be a bad idea to have it. If you should over load a airport with to much AI they will not have a place to park and you will need AFCAD in order to add parking places for them.
Just make sure you read the readme files for the PAI aircraft and for AFCAD. 8)
PAI has a user guide as to how to use the installer and a FAQ link for questions and answers most commonly asked.

READ THE README FILE THAT COMES WITH AFCAD IT TELLS YOU HOW TO USE IT 8)