Option Explicit
 
Private Type RECT
  Left As Long
  Top As Long
  Right As Long
  Bottom As Long
End Type
 
Private Declare Function PtInRect Lib "user32" (lpRect As RECT, _
  ByVal X As Long, ByVal Y As Long) As Long
Private Declare Function SetRect Lib "user32" (lpRect As RECT, _
  ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As _
  Long
 
Private X1&(), Y1&(), X2&(), Y2&()
 
Private Sub Form_Load()
 
  Dim i&
 
  ReDim X1(2), Y1(2), X2(2), Y2(2)
  With Me
    .ScaleMode = vbPixels
    .AutoRedraw = True
    For i = 0 To 2
      X1(i) = Choose(i + 1, 110, 350, 150)
      Y1(i) = Choose(i + 1, 300, 200, 310)
      X2(i) = Choose(i + 1, 307, 450, 220)
      Y2(i) = Choose(i + 1, 70, 220, 390)
      Me.Line (X1(i), Y1(i))-(X2(i), Y2(i)), vbRed
      .DrawStyle = vbDot
      Me.Line (X1(i), Y1(i))-(X2(i), Y2(i)), vbBlack, B
      .DrawStyle = vbSolid
    Next i
  End With
End Sub
 
Private Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y _
  As Single)
  Dim i&, R1 As RECT
 
  For i = 0 To UBound(X1)
    Call SetRect(R1, IIf(X1(i) < X2(i), X1(i), X2(i)), IIf(Y1(i) < Y2(i), Y1(i), _
      Y2(i)), IIf(X2(i) > X1(i), X2(i), X1(i)), IIf(Y2(i) > Y1(i), Y2(i), Y1(i)))
    If PtInRect(R1, X, Y) <> 0 Then
      Me.Caption = "Im Rechteck. Überprüfen, ob Mauszeiger auf Linie " & i
      ' ...
      Exit For ' nur rausspringen, wenn auf der Linie
    Else
      Me.Caption = "Außerhalb. Nichts rechnen."
    End If
  Next i
End Sub

Gruss,

Zardoz