There is another post on this very subject. I would suggest you read that. But I will tell you anyway since you are new and have a right to know. To get an Avatar under your name, you must have at least 15 posts. When you reach 15 posts, an Avatar option becomes available where you set up and edit your profile. You may then choose from one of the many fine Avatars the boards offer, though be warned that some of those require more than 15 posts to use, or you may upload your own. This is what I did. Mine is the Minotaur from the PSX game Gauntlet Legends. However, your avatar may only be 65x65 pixels or 15000 bytes, whichever is smaller. The only way someone could get a larger Avatar is, if Bobbi ( the webmaster/owner of these boards) agreed and I'm not to sure he would. You'd have to have a very good reason. There thats it, everything you wanted to know about Avatars, but were afraid to ask, J/K. Also, to get a custom title under your name, like some have, you must reach 700 posts.
My title says Administrator, because I am an Administrator of these boards. Take care and welcome to the PSXEmu Forums.