Noob's Guide to Custom Portraits

I recently purchased and downloaded BGEE and BG2EE. I am wondering how a player can use custom portraits for the single player game. I remember in the original games, all you had to do was make a portraits folder in the game's folder and have a .bmp file of two different sizes. Where do they go now, what size, and what format?

Thanks for any reply, and sorry if this is answered someone else. The links for the manuals aren't working for me, and a quick perusal of the forums didn't turn up what I'm looking for.