P2 mobo/case question

A friend of mine needs a case for a P3 mobo that will need to be bought. He has many many P2 cases. I'm wondering if P2 was using the ATX form factor so that we can take the case and PSU out of the picture. Thanks.

If they aren't desktop (pizzaboxes) they should be ATX. The ATX came into widespread use with the introduction of the P2.
There are a few AT slot 1 motherboards out there, but they are rare.
Of course he'd probably still need to upgrade the PSU.

Thanks for the reply.
Lots of help