how to validate Textbox input ?

Hi guys. I got a form that i ask the user to input data on it and it write it in sql server db. 2 of the field data i want their sum does not exceed a perticuler value for example 5 . How i can apply such bussiness rules in to my database and input form(at the client side). I be happy if some one show how to do this

http://i5.photobucket.com/albums/y18...07/sumform.jpg ( form pic)


insert code:

Code:

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Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim MyCommand As SqlCommand

        Dim UpdateCmd As String = "Insert Into Matches Values(" & Me.TextBox1.Text & "," & Me.TextBox2.Text & "," & Me.LstPlayer.SelectedValue & "," & Me.TextBox4.Text & "," & Me.TextBox5.Text & ")"

        MyCommand = New SqlCommand(UpdateCmd, MyConnection)
        MyCommand.Connection.Open()
        MyCommand.ExecuteNonQuery()
        MyCommand.Connection.Close()
        Server.Transfer("Match.aspx")


    End Sub

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