How To Make Sure No Other Table Writes Happen Between 2 SQL Statements ?

Ok, here is my situation.....

When someone navigates to a user's profile page on my site, I present them with a slideshow of the user's photos using the AJAX slideshow extender.  I obtain the querystring value in the URL (to determine which user's page I'm on) and feed that into a webservice via a context value where an array of photos is created for the slideshow.  Now, in order to create the array's size, I do a COUNT of all of that specific user's photos.  Then, I run another SQL statement to obtain the path of those photos in the file system.  However, during the time of that first SQL query's execution (the COUNT statement) to the time of the second SQL query (getting the paths of the photos), the owner of that profile may upload or delete a photo from his profile.  I understand this would be a very rare occurrence since SQL statements 1 and 2 will be executed within milliseconds of each other, but it is still possible I suppose.  When this happens, when I try to populate the array, either the array will be too small or too large.  I'm using SqlDataReader for this as it seems to be less memory and resource intensive than datasets, but I could be wrong since I'm a relative beginner and newbie.   This is what I have in my vb file for the webservice.....
Public Function GetSlides(ByVal contextKey As String) As AjaxControlToolkit.Slide()
     Dim dbConnection As New SqlConnection("string for the data source, etc.")

     Try
          dbConnection.Open()

          Dim memberId = CInt(contextKey)
          Dim photoCountLookupCmd As New SqlCommand _
               ("SELECT COUNT(*) FROM Photo WHERE memberId = " & memberId, dbConnection)
          Dim thisReader As SqlDataReader = photoCountLookupCmd.ExecuteReader()

          Dim photoCount As Integer
          While (thisReader.Read())
               photoCount = thisReader.GetInt32(0)
          End While
          thisReader.Close()

          Dim MySlides(photoCount - 1) As AjaxControlToolkit.Slide

          Dim photoLookupCmd As New SqlCommand _
               ("SELECT fullPath FROM Photo WHERE memberId = " & memberId, dbConnection)
          thisReader = photoLookupCmd.ExecuteReader()

          Dim i As Integer
          For i = 0 To 2
               thisReader.Read()
               Dim photoUrl As String = thisReader.GetString(0)
               MySlides(i) = New AjaxControlToolkit.Slide(photoUrl, "", "")
          Next i
          thisReader.Close()

          Return MySlides

     Catch ex As SqlException

     Finally
          dbConnection.Close()

     End Try

End FunctionI'm trying to use the most efficient method to interact with the database since I don't have unlimited hardware and there may be moderate traffic on the site.  Is SqlDataReader the way to go or do I use something else?  If I do use SqlDataReader, can someone show me how I can run those 2 SQL statements in best practice?  Would I have to somehow lock writing to that table when I start the first SQL statement, then release the lock after I execute the second SQL statement?  What's the best practice in this kind of scenario.

Thanks in advance.