Show/Hide Problem

I was working on a program that would hide a certain window using

Public Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long

and it works fine for me (Win98) but when i sent it to my friends (win2k) to test it, It gave them an overflow error. Does anyone know whats wrong or what cna i do to resolve this problem?

'Hide
x = ShowWindow(hWnd, SW_Hide)

'Show
x = ShowWindow(hWnd, SW_Show)