Two method in diffrend thread?? How?

hy,
i have method how read informatin from serial ports, and in same method, function who put information to Listbox in Form. And now, when I execute (compile) this method , they me post Erorr "Cross-thread is not ok" . "SerialPort1.ReadExisting" and " listbox.Items.Add is not and sam thread....how can I put Ithem.Add in same thread with ReadExisting...How can I use BeginInvoke method for this
Thank you
my code:
"Private Sub Form2(ByVal sender As System.Object, ByVal e As
System.IO.Ports.SerialDataReceivedEventArgs) Handles
SerialPort1.DataReceived

Dim strSerialPortData As String = SerialPort1.ReadExisting

ListBox2.Items.Add(Microsoft.VisualBasic.Left(strSerialPortData, 6))

End Sub"