The MouseMove event of the TextBox returns the cursor coordinates relativr to it. If you want to get the absolute position you can use the GetCursorPos API function or add the position of the TextBox and every parent to the coordinates.
Code:
'Module
Public Type tCoord2D
x As Long
y As Long
End Type
Public Declare Function GetCursorPos Lib "user32" Alias "GetCursorPos" (lpPoint As tCoord2D) As Long
'Code
Dim Temp as tCoord2D
'Get position
GetCursorPos Temp
Caption = Temp.x & ", " & Temp.y