<asp:DataGrid id="MonDatagrid" runat="server" AutoGenerateColumns="False">
   <Columns>
      <asp:TemplateColumn HeaderText="Colonne1">
         <ItemTemplate>
             <#Container.DataItem("nomdemacolonne")>
         </ItemTemplate>
         <EditItemTemplate>
             <asp:Textbox runat="server" width="600" maxlength="600"/>
          </EditItemTemplate>
      </asp:TemplateColumn>

procedure TWebForm1.MonDatagrid_PreRender(sender: System.Object; e: System.EventArgs);
var matextbox : TextBox ;
begin
  if MonDatagrid.EditItemIndex > -1 then
  begin
    matextbox := MonDatagrid.Items[MonDatagrid.EditItemIndex].Cells[0].Controls[0] as TextBox ;
    matextbox.Width := System.Web.UI.WebControls.Unit.Parse('4cm') ;
    // Unit etant un mot clé dans Delphi, on met sa hierarchie devant
    // on peut biensur changer d'autre propriétées de la textbox d'édition des données ;-)
  end ;
end ;

procedure TWebForm1.Mondatagrid_ItemDataBound(sender: System.Object; e: System.Web.UI.WebControls.DataGridItemEventArgs);
begin
  if not e.Item.ItemIndex = -1 then
  begin
    if e.Item.ItemIndex = 4 then
    begin
      e.Item.Cells[0].BackColor := System.Drawing.Color.Red ;
      e.Item.Cells[1].BackColor := System.Drawing.Color.Red ;
      e.Item.Cells[2].BackColor := System.Drawing.Color.Red ;
      e.Item.Cells[3].BackColor := System.Drawing.Color.Red ;
    end ;
  end ;
end ;

Mondatagrid.columns[1].visible := False ;

<asp:DataGrid id="Mondatagrid" runat="server" AutoGenerateColumns="True" 
 OnItemDataBound="Mondatagrid_OnItemDataBound"/>

procedure TWebForm1.Mondatagrid_ItemDataBound(sender: System.Object; e: System.Web.UI.WebControls.DataGridItemEventArgs);
begin
  e.Item.Cells[1].Visible := False ;
end ;

<Columns>
    <asp:TemplateColumn>
        <HeaderStyle Width="600px"></HeaderStyle>
        <ItemTemplate>
            <asp:Button id="Button1" runat="server" Text="NotreBouton"></asp:Button>
        </ItemTemplate>
    </asp:TemplateColumn>
<Columns>