<script language="javascript" type="text/javascript">
    function OpenWindow(strField)

            {

                        window.open('Details.aspx?field=' + strField, 'Details', 'width=250,height=190,resizable=yes');

            }

    </script>

           <asp:TemplateField>
                    <ItemTemplate>
                       
                        <asp:HyperLink ID="MyLink" runat="server"></asp:HyperLink>
                    </ItemTemplate>
                </asp:TemplateField>

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if(e.Row.RowType == DataControlRowType.DataRow)
        {
            HyperLink _hyperlink = e.Row.FindControl("MyLink") as HyperLink;

            if(_hyperlink != null)
            {
                _hyperlink.NavigateUrl = "javascript:;";
                _hyperlink.Text = "vai";
                _hyperlink.Attributes.Add("onclick", string.Format("OpenWindow('{0}')", GridView1.DataKeys[e.Row.RowIndex].Value));
            }
            else
            {
                Trace.Warn("Impossibile trovare l'istanza del controllo");
            }
        }
    }