The purpose of this study is to determine if atomoxetine (a common brand name is Strattera), a medicine that is used for treating older children with Attention Deficit and Hyperactivity Disorder (ADHD), is also safe and helpful for ADHD problems in young children. While atomoxetine is not approved by the FDA for use in children younger than 6 years, the FDA has given permission to study this drug in this age group.