At 8? It's hard to remember what I was like back then. I think most of the talking I'd want to do if I went back in time is giving advice to my parents, not to me! I like how I turned out, for the most part (I think I wasted alot of time before I figured out where my interests lie) I would probably do nothing for fear of affecting myself adversely (which raises a whole slew of questions about just what would happen to me, but these are outside the scope of the question)
Reaction: Hard to guage. I don't know how I stack up with my idea of what I'd be like at this age. Probably awe and open mindedness. I was a pretty quick kid, but at 8, I don't know how well I'd remember or implement any of my own advice!
Advice: The advice would consist of showing myself that I do, in fact, turn out to be superior to the kids I grew up with... and attempting to instill an interest in the things that make me so early on. Probably I would bring with me some classical music and maybe even Serial Experiments: Lain. I would steer myself away from the other kids and attempt to isolate myself from any sort of social life (I'm afraid now I'm addicted, but in this scenario, I would not have to be)... the conversation would go:
"You know that kid down the block? Stay away from him. Later, he's gonna turn out real bad... he's gonna attack another friend of yours with a machete one night. Try to kill him. In a few years, this neighborhood isn't going to be as pretty as it is now. Keep your nose out of it! You're better off on your own anyway, don't waste your time with that trash. Just listen to this guy, Liszt... would you rather spend your time in fights with "friends" who don't share your interests... or would you rather devote your time to doing great things like this guy did? ... I thought so."