Our behaviour with HIV infected person must be normal. There are no chances of acquiring AIDS by having normal behaviour with the HIV positive person. HIV can pass only through body fluids and blood from HIV infected person to the other normal person. Similarly, the needles or syringes used by HIV infected person can cause the infection of HIV to the other person.
Such ways of contamination should always be avoided. The sexual contact or the blood transfusion with HIV positive person should always be avoided. But the normal behaviour such as hand-shake, eating together, studying in the same class will not matter at all in the transmission of AIDS.