'クラス登録を削るとこんなもん

Dim wcx As WNDCLASSEX
wcx.cbSize = SizeOf(WNDCLASSEX)
wcx.lpfnWndProc = AddressOf(wndproc)
wcx.hInstance = GetModuleHandle(NULL)
wcx.hbrBackground = GetStockObject(WHITE_BRUSH)
wcx.lpszClassName = "DEFAULTCLASS"

Dim hMainWnd As HWND
hMainWnd = CreateWindowEx(0,RegisterClassEx(wcx),"test",WS_OVERLAPPEDWINDOW Or WS_VISIBLE,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,0,NULL,GetModuleHandle(NULL),0)