Pass the name of the slide and the presentation in which to perform search
to this function and it will return the slideindex for that slide.
' ----------------------------------------------------------------------------
Sub Sample()
Dim lngIndex As Long
lngIndex = GetSlideIndexFromName("Slide1", ActivePresentation)
If lngIndex = 0 Then
   MsgBox "Could not find slide with provided name.", vbExclamation
Else
   'Perform operation here...
End If
End Sub

Function GetSlideIndexFromName(Name As String, oPres As Presentation) As
Long
Dim oSld As Slide
For Each oSld In oPres.Slides
   If oSld.Name = Name Then
       GetSlideIndexFromName = oSld.SlideIndex
       Exit Function
   End If
Next oSld
End Function
' ----------------------------------------------------------------------------