Hello! Just bought the game for the first time. I've played all the old school CRPG's except for this one, terrible I know. That being said, I saw on the bonus content after my purchase from GOG that theres an AVATAR download. Where exactly do I unzip these files to in the PST folder? Thanks. I'm excited to play

You mean the bonus content avatars? No, it's just avatars for you to use, not to use them in game.

<<------------ you can use them here as this little picture that shows up next to your posts.

As your avatar, you know...

Well, that was misleading. I was hoping to download alternative avatars for the game itself.

GOG used to have Avatar picture (i.e. for use here on the forum) for nearly every game of their catalogue, so it's for historic reasons the description is unclear. If you see something about Avatars on GOG most of the it will simply be pictures for use on forums.
By the way, all characters in Planescape Torment have fixed portraits, so bonus Avatars wouldn't make sense. But that isn't something you would know if you never played the game, Maybe GOG should be thinking about clarifying the descriptions for bonus Avatars as they seem to be getting rarer and new customers wouldn't often times not know what they are.

You'll both be glad to know that Tchos' portrait mod lets you choose which portraits/avatars you want to replace. The quality varies, but Annah and Fall-From-Grace's are really great.