Option Explicit
 
Private Sub Form_Load()
  TreeView1.Nodes.Add(, tvwFirst, , "Main").Tag = "Tooltiptext für den obersten" & _
    "Eintrag..."
  TreeView1.Nodes.Add(1, tvwChild, , "Item1").Tag = "Tooltiptext für den 2." & _
  "Eintrag..."
  TreeView1.LineStyle = tvwRootLines
End Sub
 
Private Sub TreeView1_MouseMove(Button As Integer, Shift As Integer, x As _
  Single, y As Single)
  Dim sTip As String
 
  ' Mausposition auswerten
  If TreeView1.HitTest(x, y) Is Nothing Then
    sTip = ""
  Else
    sTip = TreeView1.HitTest(x, y).Tag & " - " & TreeView1.HitTest(x, y).Text
  End If
 
  ' Tooltip setzen
  TreeView1.ToolTipText = sTip
End Sub

Viel Spass,
R@lf