<form id="form1" runat="server" DefaultFocus="formVw$txtName">
    <div>
        <asp:FormView ID="formVw" runat="server">
            <ItemTemplate>
                Name:
                <asp:TextBox ID="txtName" runat="server"
                    Text='<%# Eval("FirstName") + " " + Eval("LastName") %>' />
            </ItemTemplate>
        </asp:FormView>
    </div>
</form>

TextBox tb = this.FindControl("form1$formVw$txtName") as TextBox;
if (tb != null)
{
    //Access TextBox control
}

<form id="form1" runat="server">
    Search Text: <asp:TextBox ID="txtSearch" runat="server" />
    <asp:RequiredFieldValidator ID="valSearch" runat="Server"
      ControlToValidate="txtSearch" ValidationGroup="SearchGroup" />
    <asp:Button ID="btnSearch" runat="server" Text="Search"
      ValidationGroup="SearchGroup" />
    ....
    Other controls with validators and buttons defined here
</form>