我们知道ClipCursor可以将指针限制到指定区域，那么如何反其道而为之，禁止鼠标进入某个区域呢，答案是用鼠标钩子，在WIN NT 4.0 SP3以上系统可以用WH_MOUSE_LL这个钩子实现，这个钩子的特殊之处是不需要用dll，另外，这个钩子用到了一个结构体，简单说明一下：
typedef struct {
    POINT pt;
    DWORD mouseData;
    DWORD flags;
    DWORD time;
    ULONG_PTR dwExtraInfo;
} MSLLHOOKSTRUCT, *PMSLLHOOKSTRUCT;

Members

pt

Specifies a POINT structure that contains the x- and y-coordinates of the cursor, in screen coordinates.

mouseData

If the message is WM_MOUSEWHEEL, the high-order word of this member is the wheel delta. The low-order word is reserved. A positive value indicates that the wheel was rotated forward, away from the user; a negative value indicates that the wheel was rotated backward, toward the user. One wheel click is defined as WHEEL_DELTA, which is 120.

If the message is WM_XBUTTONDOWN, WM_XBUTTONUP, WM_XBUTTONDBLCLK, WM_NCXBUTTONDOWN, WM_NCXBUTTONUP, or WM_NCXBUTTONDBLCLK, the high-order word specifies which X button was pressed or released, and the low-order word is reserved. This value can be one or more of the following values. Otherwise, mouseData is not used.

XBUTTON1

The first X button was pressed or released.

XBUTTON2

The second X button was pressed or released.

flags

Specifies the event-injected flag. An application can use the following value to test the mouse flags.

Value	Purpose
LLMHF_INJECTED	Test the event-injected flag.

0

Specifies whether the event was injected. The value is 1 if the event was injected; otherwise, it is 0.

1-15

Reserved.

time

Specifies the time stamp for this message.

dwExtraInfo

Specifies extra information associated with the message.

Public Type RECT
    Left As Long
    Top As Long
    Right As Long
    Bottom As Long
End Type

Private Type POINTAPI
   x As Long
   y As Long
End Type

Private Type MSLLHOOKSTRUCT
    pt As POINTAPI
    mouseData As Long
    Flags As Long
    time As Long
    dwExtraInfo As Long
End Type

Public hHook As Long
Public hRT As RECT
Public Sub EnableHook(hRect As RECT)
    hRT = hRect
    If hHook = 0 Then
       hHook = SetWindowsHookEx(WH_MOUSE_LL, AddressOf HookProc, App.hInstance, 0)
    End If
End Sub
Public Sub FreeHook()
If hHook <> 0 Then
   Call UnhookWindowsHookEx(hHook)
   hHook = 0
End If
End Sub

Public Function HookProc(ByVal nCode As Long, ByVal wParam As Long, ByVal lparam As Long) As Long
    Dim typMHS As MSLLHOOKSTRUCT, pt As POINTAPI
    If nCode < 0 Then
       HookProc = CallNextHookEx(hHook, nCode, wParam, lparam)
       Exit Function
    End If
    If wParam = WM_MOUSEMOVE Then
        Call CopyMemory(typMHS, ByVal lparam, LenB(typMHS))
        pt = typMHS.pt
        If PtInRect(hRT, pt.x, pt.y) <> 0 Then
            HookProc = 1 '取消原本要完成的動作
        Else
            Form1.Caption = "mouse Cursor at " + CStr(pt.x) + "," + CStr(pt.y)
            HookProc = 0 '令待完成的動作繼續完成
        End If
    End If
End Function

窗体代码：
Option Explicit
Const HWND_TOPMOST = -1
Const HWND_NOTOPMOST = -2
Const SWP_NOSIZE = &H1
Const SWP_NOMOVE = &H2
Const SWP_NOACTIVATE = &H10
Const SWP_SHOWWINDOW = &H40
Private Declare Sub SetWindowPos Lib "user32" (ByVal hWnd As Long, ByVal hWndInsertAfter As Long, ByVal x As Long, ByVal y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long)

Private Sub Form_Activate()
   '设置窗口为TOPMOST窗口，目的是便于观察
    SetWindowPos Me.hWnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOACTIVATE Or SWP_SHOWWINDOW Or SWP_NOMOVE Or SWP_NOSIZE
End Sub
Private Sub Form_Load()
    Dim RT As RECT
    With RT
    .Left = 0
    .Right = 400
    .Top = 0
    .Bottom = 300
    End With
    EnableHook RT
End Sub