In the example below you can use frm_detail.SetFocus to put your "popup"
form on top.  Also, you can hide and display it with frm_detail.Visible =
True/False

Open a sub form from a parent form and set up two way calling.

' In a module
Public Function IsOpen(strForm As String) As Boolean
   IsOpen = (SysCmd(acSysCmdGetObjectState, acForm, strForm) > 0)
End Function

' In frm_Calling
Private frm_detail As Form_frm_detail

   If IsOpen("frm_detail") And Not frm_detail Is Nothing Then
       frm_detail.CallingName = strTargetKeyString
   Else
       DoCmd.OpenForm "frm_detail", _
           DataMode:=acFormEdit, _
           WindowMode:=acWindowNormal, _
           OpenArgs:=Trim(CStr(lngRecordID)) & "^" & strTargetKeyString &
"^" & Me.Name
       Set frm_detail = Application.Forms("frm_detail")        
   End If
   
' If the calling form is a subform then the above open must use the parent
form name
' Use Parent.Name rather than Me.Name

' ****In frm_detail*****

Private ParentForm As Form
Private ParentFormName As Variant
Private lngRecordID As Long

Property Set ParentObject(fValue As Form)
   Set ParentForm = fValue
   ParentFormName = ParentForm.Name
End Property

Property Let CallingName(vValue As Variant)
   ' put code in here to initialize your form
   ' run a parameterized query to retrieve the desired records
   ' set default values for controls
End Property

Private Sub Form_Load()
   Dim lngOne As Long
   Dim vTargetKey As Variant
   Dim vCallingForm As Variant
   Dim vInstanceID As Variant
   
   If Not IsNull(Me.OpenArgs) Then
       
       lngOne = 1
       vInstanceID = Trim(Nz(Left(Me.OpenArgs, InStr(lngOne, Me.OpenArgs,
"^") - 1), ""))
       lngOne = InStr(lngOne, Me.OpenArgs, "^") + 1
       vTargetKey = Trim(Nz(Mid(Me.OpenArgs, lngOne, InStr(lngOne,
Me.OpenArgs, "^") - lngOne), ""))
       lngOne = InStr(lngOne, Me.OpenArgs, "^")
       vCallingForm = Trim(Nz(Right(Me.OpenArgs, Len(Me.OpenArgs) -
lngOne), ""))
       Set ParentObject = Application.Forms(vCallingForm)
' If the calling form is a subform use the following
'        Set ParentObject =
Application.Forms(vCallingForm).subformcontrolname.Form
       lngRecordID = CLng(Nz(vInstanceID, "0"))
       CallingName = vTargetKey ' A method to initialize the form
       
   End If ' If Not IsNull(Me.OpenArgs) Then
End Sub

' Now each form can call methods in the other