I have been asked several times how to implement a Confirm Delete on the delete button of a DetailsView. Here is how you do it...
 
Put this in the “DetailsView_ItemCreated” event then replace the "DetailsView2" with your DetailsView ID and it should work fine.  Make sure you add the event onto your DetailsView and if the command bar is not the last element in the rows collection - you will need to update the index.

// Test FooterRow to make sure all rows have been created
        if (DetailsView2.FooterRow != null)
        {
            // The command bar is the last element in the Rows collection
            int commandRowIndex = DetailsView2.Rows.Count - 1;
            if (commandRowIndex > 0)
            {
                DetailsViewRow commandRow = DetailsView2.Rows[commandRowIndex];

                // Look for the DELETE button
                DataControlFieldCell cell = (DataControlFieldCell)commandRow.Controls[0];
                foreach (Control ctl in cell.Controls)
                {
                    LinkButton link = ctl as LinkButton;
                    if (link != null)
                    {
                        if (link.CommandName == "Delete")
                        {
                            link.ToolTip = "Click here to delete";
                            link.OnClientClick = "return confirm('Do you really want to delete this record?');";
                        }
                    }
                }
            }
        }