Modulo.bas
Type RECT
   left As Integer
   top As Integer
   right As Integer
   bottom As Integer
End Type

Form1.frm
Option Explicit
Declare Sub GetWindowRect Lib "USER" (ByVal hWnd%, lpRect As RECT)
Declare Sub ClipCursorClear Lib "USER" Alias "ClipCursor" (ByVal lpRect&)
Declare Sub ClipCursor Lib "USER" (lpRect As RECT)

Sub Form_Resize ()
    Dim lpRect As RECT

    Call GetWindowRect(Me.hWnd, lpRect)
    Call ClipCursor(lpRect)
End Sub

Sub Form_Unload (Cancel As Integer)
    Call ClipCursorClear(0&)
End Sub