1. put a folder named avatars in the phpBB2/images/ directory.
2. put 2 folders inside the avatar folder |upload + gallery|
3. put a folder inside the gallery folder with a name for the group of avatars you'll be putting here for your users to look through to use
then you would upload all your avatars that would go in this category into this folder
and for every category of avatars you have, you can make another folder in the gallery directory for them
etc. etc. etc.
this way when someone goes to the gallery to get an avatar, the avatars are organized by categories.
hope this helped.
EDIT - I forgot to tell you why you need the upload folder in there. it's for your users to upload their own avatars if you allow them to do this.
"I'm just a figment of your imagination."