Please ignore... I should've tested my own theory.  This seems to work.

In the ExcelService class, I have
try
            {
                m_frm = new ContractSelectionForm( mode );
                m_frm.Closed +=new EventHandler(m_frm_Closed);
                EnableWindow( new IntPtr(base.GetExcelhWnd()), false);
                m_isWndEnabled = false;
                m_frm.ShowDialog();
            }
            catch (Exception exc)
            {
                throw new AdapterServiceException(exc);
            }
            finally
            {
                if (!m_isWndEnabled)
                {
                    EnableWindow( new IntPtr(base.GetExcelhWnd()), true);
                    m_isWndEnabled = true;
                }
            }

and in the form, I have

        private void ContractSelectionForm_Activated(object sender,
System.EventArgs e)
        {
            if( !GetForegroundWindow().Equals( this.Handle ) )
            {
                ShowWindow(this.Handle, SW_RESTORE);
                SetForegroundWindow(this.Handle);
            }
        }

However, this creates another problem.  While the dialog is open and
the user clicks around in the Excel instance, hte mouseClicks seem to
get queued up, only to take place when the dialog is dismissed. Is
there a workaround for this?

Thanks
Thanks