You could use api_SetWindowPos:
As Vertigo and Neo mentioned, for this command to be available, you need to put 'user32.decls' in the \userlibs folder of Blitz.
Graphics3D 640, 480, 0, 3 hwnd = SystemProperty$("apphwnd") api_SetWindowPos(hwnd, 0, 0, 0, 640, 480, $40) WaitKey()
As Vertigo and Neo mentioned, for this command to be available, you need to put 'user32.decls' in the \userlibs folder of Blitz.