RichTextBox1.SelectionStart = rtb_chatout.TextLength
RichTextBox1.Focus()

Private Declare Function SendMessage Lib "user32" _
    Alias "SendMessageA" ( _
    ByVal hwnd As Long, _
    ByVal wMsg As Long, _
    ByVal wParam As Long, _
    ByVal lParam As Long) As Long
 
Private Const WM_VSCROLL = &H115
Private Const SB_ENDSCROLL = 8
 
 
 
SendMessage(RichTextBox1.Handle.ToInt32, WM_VSCROLL, SB_ENDSCROLL , 0&)