Grid view help

Dear Friends

I am making an application in which a gridview take a parameter from textbox to populate a data. my question is how can i make it display in running. i mean i want when i click a button. the gridview should display the data filtered on the basis of textbox. and i should be able to select the rows too. the code i have done so far is like this. it shows the data but it do not allow me to select the data

Code:

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Sub populate_Grid()
        'This code is used to populate the data
        Try

            Dim sql_connection As New SqlConnection("Data Source=cc;Initial Catalog=Raw_dspatch;User ID=xxx;Password=fff")
            Dim sql_command As New SqlCommand("SELECT PO_No, Srno, Item_Code, Detail, Order_Qty, Rate FROM ER_Purchase_Order WHERE PO_No = '" & txtPo_no.Text & "'", sql_connection)
            Dim da As New SqlDataAdapter(sql_command)
            Dim dt As New DataTable
            da.Fill(dt)
            GridView1.DataSource = dt
            GridView1.DataBind()










        Catch ex As Exception
            MsgBox(ex.ToString)

        End Try
    End Sub

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Please help me. its urgent

Sample code given here: http://aspadvice.com/blogs/joteke/ar.../07/14576.aspx

(To let you select a row)