Something

// in LoginViewController

    homeViewController = [[HomeViewController alloc] initWithNibName:@"HomeViewController" bundle:nil];
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    [[window subviews] makeObjectsPerformSelector:@selector(removeFromSuperview)];
    [window addSubview:homeViewController.view];
    [homeViewController release];

// in HeaderView (a UIView subclass), which HomeViewController adds

    LoginViewController *loginViewController = [[LoginViewController alloc] initWithNibName:@"LoginViewController" bundle:nil];
    UIWindow *window = [UIApplication sharedApplication].keyWindow;
    [[window subviews] makeObjectsPerformSelector:@selector(removeFromSuperview)];
    [window addSubview:loginViewController.view];
    [loginViewController release];

// this won't work. it says *** -[LoginViewController performSelector:withObject:withObject:]: message sent to deallocated instance 0x1db2a0