The following will get the currently selected text from an e-mail message in Outlook. If you are familiar with Word VBA then wdDoc is the message body and can be processed pretty much as a document in Word.
Sub test()
Dim OutApp As Object
Dim OutMail As Object
Dim olInsp As Object
Dim wdDoc As Object
Dim strText As String

    On Error Resume Next
    'Get Outlook if it's running
    Set OutApp = GetObject(, "Outlook.Application")

    'Outlook wasn't running, so cancel
    If Err <> 0 Then
        MsgBox "Outlook is not running so nothing can be selected!"
        GoTo lbl_Exit
    End If
    On Error GoTo 0

    Set OutMail = OutApp.ActiveExplorer.Selection.Item(1)
    With OutMail
        Set olInsp = .GetInspector
        Set wdDoc = olInsp.WordEditor
        strText = wdDoc.Application.Selection.Range.Text
    End With
    MsgBox strText
lbl_Exit:
    Set OutMail = Nothing
    Set OutApp = Nothing
    Set olInsp = Nothing
    Set wdDoc = Nothing
    Exit Sub
End Sub