int nFullWidth=GetSystemMetrics(SM_CXSCREEN);
int nFullHeight=GetSystemMetrics(SM_CYSCREEN);
this->SetWindowPos(&wndTopMost,0,0,nFullWidth,nFullHeight,SWP_NOMOVE);
or
::SetWindowPos(AfxGetMainWnd()->m_hWnd,HWND_TOPMOST,0,0,nFullWidth,nFullHeight,SWP_NOMOVE);
上面两句话是等效的都可以实现掩盖任务栏的目的