SendMessage Not working

[Halsafar]

Alright, my SendMessage() is not working.

    Index = SendMessage(m_hwnd, LB_ADDSTRING, 0, (LPARAM)Item);
    SendMessage(m_hwnd, LB_SETITEMDATA, Index, (LPARAM)Item); 

The first SendMessage is suppose to return the index of the added string...Always 0, no matter what, which is wrong compared to other code I've seen.

     LRESULT Count = SendMessage(m_hwnd, LB_GETCOUNT,0,0);
    LRESULT Index = SendMessage(m_hwnd, LB_GETSEL,0,0);
    LRESULT iLength = SendMessage(m_hwnd, WM_GETTEXTLENGTH,(WPARAM)Index,0); 

Both of those also always return 0, no matter how much data is on the listbox.
IT ALWAYS RETURNS 0....WHY? I'm searching msdn, gamedev, vbforums....and I am getting no where.