HWND and ScreenToClient issues.

Hi,

I am writing an application for Pocket PC handset. I have few controls
on my PropertyPage. I am handling the WM_SIZE event to adjust the
controls to center of the display area on the screen, so that even if
the screen size changes ( by handset screen rotate), the controls are
always in the center of the screen.
Here is what i do:

void CSmartBuddies::OnSize(UINT nType, int cx, int cy)
{
    CPropertyPage::OnSize(nType, cx, cy);

    // TODO: Add your message handler code here

        RECT rcClient;
    ::GetClientRect(this->m_hWnd, &rcClient);

    HWND hwndCtl = ::GetDlgItem(this->m_hWnd, ID_OF_A_CONTROL_ON_DIALOG);

    RECT rcCtl;
    ::GetWindowRect(hwndCtl, &rcCtl);

         int nLeft, nTop, nWidth, nHeight;

        nLeft = ((rcClient.right - rcClient.left) - (rcCtl.right -
rcCtl.left))/2;
    nWidth = rcCtl.right - rcCtl.left;
    nHeight = rcCtl.bottom - rcCtl.top;

       CWnd mywnd; // Line 1
        mywnd.Attach(this->m_hWnd); // Line 2
        mywnd.ScreenToClient(rcCtl); // Line 3

         nTop = rcCtl.top ; // PROBLEM HERE

         hwndDlg = myWnd.Detach(); // Line 4

        ::MoveWindow(hwndCtl, nLeft, nTop, nWidth, nHeight, TRUE);

}

Now, If I remove lines "Line 1, 2, 3, 4" and hardcode nTop to some
value like 15, then the control is in centre of the dialog and
everything is fine (for control ID_OF_A_CONTROL_ON_DIALOG) .
 I checked with rcCtl.top in line "Problem here" after adding "Line
1, 2, 3, 4". Its value is also 15. But, The page does not appear
correctly. Control is not in center either. Controls of other property
pages are overlapping over this page. Can anybody please explain what
I should do so that it works fine. Is there something wrong with
Attach() and Detach() code.

Thanks in advance,
Regards,
Triveni Prabhu