Code:
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        With rtfMircClone
            .SelectionStart = Len(.Text)
            .SelectedText = "I'm some server data :TKCHATACHAT001 613 127.0.0.1 6667" & vbCrLf
            .SelectedText = "i'm the next row of data" & Chr(10) '// same effect as vbcrlf
        End With
    End Sub

    Private Sub rtfMircClone_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles rtfMircClone.MouseUp
        rtfMircClone.SelectionStart = Len(rtfMircClone.Text)
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        rtfMircClone.AppendText("extra text getting appended to end of data" & Chr(10))
    End Sub
you need to set hide selection to FALSE so that the richtextbox scrolls when the text reaches the bottom of the visible area of it.