add a new module to your project and slap this in it

Code:
Option Explicit

Private Type POINTAPI
        x As Long
        y As Long
End Type

Private Declare Function GetCursorPos Lib "user32" (lpPoint As POINTAPI) As Long
Private Declare Function ScreenToClient Lib "user32" (ByVal hwnd As Long, lpPoint As POINTAPI) As Long


Public Function IsCursorInBox(ByVal x1 As Single, ByVal y1 As Single, ByVal x2 As Single, ByVal y2 As Single, Window As Object)

Dim apiPos As POINTAPI
Dim x As Single
Dim y As Single
Dim retval As Boolean

On Error GoTo ERR_IsCursorInBox:

GetCursorPos apiPos

ScreenToClient Window.hwnd, apiPos

x = Window.ScaleX(apiPos.x, Window.ScaleMode, vbPixels)
y = Window.ScaleY(apiPos.y, Window.ScaleMode, vbPixels)

retval = x > x1
retval = retval And x < x2
retval = retval And y > y1
retval = retval And y < y2

IsCursorInBox = retval

Exit Function

ERR_IsCursorInBox:

Err.Raise 13

End Function
Window is the window that the coordinates are based in, for example if the coords are relitive to Picture1 then Window would be Picture1.

It Only works on Forms and Pictureboxes.