Lucas:
It's awesome that you want to help your brother. Good for you for not giving up in a hard situation.
I don't know either of you, so if what I say sounds completely wrong, feel free to ignore it. But in my experience, kids who show the "symptoms" your brother does generally believe that no one can/will ever love them. They figure that the best they can hope for is attention, and so they do whatever it takes to get attention (Aquire stuff, throw tantrums, do things they know will anger their parents.) It's entirely possible that this feeling was caused/exacerbated by problems in his childhood: epilepsy caused him to think he's a "freak", crooked teeth and braces made him think he's ugly, and a high-tension divorce drove home the lesson that there is no safety even among those you love most.
These people (kids and adults) also have a really hard time with personal development. The reason is that PD requires examining your life, finding the weak points, and working to improve them. When your life involves this much pain, it's easier, less painful, and less scary to pretend that the problems don't exist, and play video games instead. Add fear of the truth to fear of being unloved, and PD can become well-nigh impossible.
I think the guitar idea is great -- it would also be great to see about creating music together, maybe making some kind of band. The most important thing you can do for your brother right now is let him know that you love and respect him no matter what. Helping him with guitar, asking how he feels and really listening, giving the best advice you can, emails/IMs on the days you're not together, hugs... whatever you think would best help him know that he has at least one ally in his desire to be a good person and make his life better.
If he expresses interest, or you think you know of a PD subject that would specifically interest him, you could point him to these forums or to a book or website that might relate. Even just sending a link to a single blog post of Steve's could help. Shoot him an email that says, "Hey, I thought this was cool, thought I'd share." Then he has the opportunity to look into it and explore without having to tell anyone what he's doing and risk getting laughed at or scorned.
Just my thoughts. Good luck to both of you. If I can help, feel free to PM me.
Amanda