Public Class Form1
  Dim x1, y1, x2, y2, w, h As Integer
  Dim dragRec As Boolean
  Dim memX, memY As Integer
 
  Private Sub Form1_Load _
             (sender As Object, e As EventArgs) Handles Me.Load 
  x1 = 80: y1 = 45: x2 = 240: y2 = 135 : w = 160: h = 90
  End Sub
 
  Private Sub pb1_MouseDown _
             (ByVal sender As Object, ByVal e As _
             System.Windows.Forms.MouseEventArgs) Handles pb1.MouseDown
  dragRec = True
  memX = e.X: tb1.Text = memX
  memY = e.Y: tb2.Text = memY
  End Sub
 
  Private Sub pb1_MouseMove _
             (ByVal sender As Object, ByVal e As _
             System.Windows.Forms.MouseEventArgs) Handles pb1.MouseMove
  If Not dragRec Then Exit Sub
 
  x1 = x1+(e.X-memX) 
  memX = e.X
  y1 = y1+(e.Y-memY) 
  memY = e.Y
  x2 = x1+w
  y2 = y1+h
 
  If x1 < 0 OR y1 < 0 OR x2 > pb1.Width-3 OR y2 > pb1.Height-3 Then Exit Sub
 
  pb1.Refresh
  End Sub
 
  Private Sub pb1_MouseUp_
             (ByVal sender As Object, ByVal e As _
             System.Windows.Forms.MouseEventArgs) Handles pb1.MouseUp
  dragRec = False
  End Sub
 
 
 
  Private Sub pb1_Paint _
             (sender As Object, e As PaintEventArgs) Handles pb1.Paint 
  e.Graphics.DrawRectangle(Pens.Red, x1, y1, x2-x1, y2-y1)
  End Sub
End Class

Zitat:

Warum wird das Rechteck manchmal nicht bis an den Rand geschoben????

Class Form1
 
  Dim dragRec As Boolean, mPos As Point
  Dim Rect As New Rectangle(80, 45, 160, 90)
 
  Private Sub pb1_MouseDown(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseDown
    If e.Button = MouseButtons.Left AndAlso Rect.Contains(e.Location) Then
      dragRec = True
      mPos = e.Location
      TB1.Text = mPos.ToString
    End If
  End Sub
 
  Private Sub pb1_MouseMove(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseMove
    If Not dragRec Then Exit Sub
    Dim p As Point = Rect.Location + (e.Location - mPos) 'neue Rechteck-Position
    mPos = e.Location 'aktuelle Mausposition merken
    If p.X < 0 Then p.X = 0
    If p.Y < 0 Then p.Y = 0
    If p.X + Rect.Width > PB1.Width - 3 Then p.X = PB1.Width - 3 - Rect.Width
    If p.Y + Rect.Height > PB1.Height - 3 Then p.Y = PB1.Height - 3 - Rect.Height
    If p <> Rect.Location Then
      Rect.Location = p
      PB1.Refresh()
    End If
  End Sub
 
  Private Sub pb1_MouseUp(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseUp
    dragRec = False
  End Sub
 
  Private Sub pb1_Paint(sender As Object, e As PaintEventArgs) Handles PB1.Paint
    e.Graphics.DrawRectangle(Pens.Red, Rect)
  End Sub
 
End Class