How To Access Data Using SqlDataSource

Hello all,
I have what I think should be a simple problem to solve but I just don't quite understand what to do (
.NET Framework Developer Center confused me :( ).

My code should load the highest SiteID, known as Last_ID into the siteIdBox when the form is in insert mode.  My difficulty is in understanding how to use the sqlDataSource correctly.
  Dim dsLastId As New SqlDataSource()
Dim siteIdBox As TextBox
Dim dsmLastId As SqlDataSourceMode

If FV_Site.CurrentMode = FormViewMode.Insert Then
Try
dsLastId.ConnectionString = ConfigurationManager.ConnectionStrings("AquaConnectionString1").ToString
dsLastId.SelectCommandType = SqlDataSourceCommandType.Text
dsLastId.SelectCommand = "SELECT MAX(Site_ID) AS Last_ID FROM Tbl_Site"

dsmLastId = SqlDataSourceMode.DataReader

siteIdBox.Text = dsmLastId.?????

Finally
dsLastId = Nothing
End Try
End If  
If anyone could tell me the code for getting the value from the select statement into the textbox, I would be most grateful.
Thank you, m00sie.