call a dialog box by using a button in another dialogbox

Add another dialog resource to your project and a handler for the button of your first dialog. In your handler call the second dialog. What is the problem exactly?

[edit]
In your dialog handler:

BOOL OnCommand(HWND		hDlg,		// handle to the dialog window
               int		nCmdId,		// ID value of the command entity (Menu or Accelerator)
               HWND		hWndCtl,	// HWND of control window
               UINT		codeNotify	// 0==Menu, 1==Accelerator
               )
{
    // Take action according to nCmdId
    switch (nCmdId)
    {
    case ID_xxx: // to call second dialgo
        DialogBox(GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_DIALOG2), hDlg, (DLGPROC)Dlg2Handler);
        break;

// other command handlers ...

    default:
        // command not handled here
        return FALSE;
    }

    return TRUE;	// for all commands that have been handled
}

LRESULT CALLBACK DlgProc(HWND		hDlg,		// handle to the main dialog window
                         UINT		uMessage,	// windows message code value
                         WPARAM		wParam,		// parameter associated with the message
                         LPARAM		lParam		// parameter associated with the message
                         )
{
    switch (uMessage)
    {
    case WM_INITDIALOG:
        return OnInitDialog(hDlg, (HWND)wParam, lParam);

    case WM_COMMAND:
        return OnCommand(hDlg, LOWORD(wParam), (HWND)lParam, HIWORD(wParam));

    case WM_SYSCOMMAND:
        return OnSysCommand(hDlg, wParam, LOWORD(lParam), HIWORD(lParam));
    }

    return FALSE;
}

[/edit]