S.D.
Right, they are just like other kids, which means no hitting. I assume you are another country based on your language and question about "punishing here". But really, children are all the same and should be treated with respect and dignity. It has been proven time and time again that spanking or smacking DOES NOT teach a child right from wrong. Get a book like Dr. Sears' "The Discipline Book" and learn how to lovingly correct your child's behavior. I know people always say "I got spanked and I turned out fine" but 50 years of research says otherwise. It's hard to find a child psychologist or behaviorist who would agree that hitting a child teaches anything more than "if you don't do what I want I will hurt you".
Time out is good. Taking things away, both objects and privileges helps. If he hits his brother with a toy, take away that toy. If he doesn't do what you tell him to, no TV for the rest of the day.
Here's a good link:
http://askdrsears.com/html/6/T060100.asp
Good Luck:)