Yes I know that for WM6.5 there is a Aygshell call right for this, SHDeviceLockAndPrompt, but one thing that works for all of the WM lockable devices is simply this:
int WINAPI WinMain( HINSTANCE hInstance,      HINSTANCE hPrevInstance,      LPTSTR    lpCmdLine,      int       nCmdShow) {  keybd_event(VK_F22, 0, 0, 0);  keybd_event(VK_F22, 0, KEYEVENTF_KEYUP, 0);

 return 0; }
I hope this helps!