Saving Data To SQL Data Base

Hi,
I'm using the following code to open a data base and show it's content
in a Data Grid View
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Code
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Imports System.Data.SqlClient

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load

Dim conn As New SqlConnection("Data
Source=./wideserver;Path="c:/cct.mdf";User
Id=username;Password=Password;")
Using (conn)
conn.Open()
Dim com As SqlCommand = conn.CreateCommand()
Using (com)
com.CommandType = CommandType.Text

com.CommandText = "Select * From users"
Dim da As New SqlDataAdapter(com)
Using (da)
Dim dt As New DataTable("usertable")
Using (dt)
da.Fill(dt)
Dim dgv As New DataGridView()
dgv.Dock = DockStyle.Fill
dgv.DataSource = dt
Me.Controls.Add(dgv)
End Using
End Using
End Using
End Using
End Sub
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end code
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The following code allow me to see the table data in a Data Grid View
but now i want to save the changes in the table (after making
modifications in the dgv)
i use : dta.update(dt)
but that don't work !!!!!!
Any Help and thanks a lot
Omar Abid
www.omarabid.uni.cc