Load page in IFRAME based on TreeView node selection

<asp:TreeView ID="TreeView1" class="leftpaneltree" runat="server" ImageSet="Arrows"
                                        NodeIndent="7" ExpandDepth="0">
                                        <HoverNodeStyle Font-Underline="True" ForeColor="#5555DD" />
                                        <Nodes>
                                            <asp:TreeNode Text="User" Value="User" NavigateUrl="User/Users.aspx"
                                                 Value="">
                                                <asp:TreeNode Text="Admin" Value="Admin" NavigateUrl="User/Admin.aspx">
                                                </asp:TreeNode>
                                                <asp:TreeNode Text="User" Value="User" NavigateUrl="User/User.aspx">
                                                </asp:TreeNode>
                                            </asp:TreeNode>
                                            <asp:TreeNode NavigateUrl="Department/Department.aspx" Text="Department"
                                                Value="Department">
                                                <asp:TreeNode NavigateUrl="Department/Sales.aspx" Text="Sales"
                                                    Value="Sales"></asp:TreeNode>
                                                <asp:TreeNode NavigateUrl="Department/Purchase.aspx" Text="Purchase"
                                                    Value="Purchase"></asp:TreeNode>
                                                <asp:TreeNode NavigateUrl="Department/Marketing.aspx" Text="Marketing"
                                                    Value="Marketing"></asp:TreeNode>
                                            </asp:TreeNode>
                                        </Nodes>
                                        <NodeStyle Font-Names="Tahoma" Font-Size="10pt" ForeColor="Black" HorizontalPadding="2px"
                                            NodeSpacing="0px" VerticalPadding="0px" />
                                        <ParentNodeStyle Font-Bold="False" />
                                        <SelectedNodeStyle Font-Underline="True" ForeColor="#5555DD" HorizontalPadding="0px"
                                            VerticalPadding="0px" />
                                    </asp:TreeView>
 <script language="javascript" type="text/javascript">
        assignTreeNodeEvent();
        function assignTreeNodeEvent() {
            var tree = document.getElementById('<%=TreeView1.ClientID %>');
            var nodes = tree.getElementsByTagName('a');
            for (var n = 0; n < nodes.length; n++) {
                var url = nodes[n].getAttribute('href');
                if (url.indexOf(".aspx") > 3) {
                    nodes[n].setAttribute('href', '#');
                    var strclick = "changePage('" + url + "')";
                    nodes[n].setAttribute('onclick', strclick);
                }
            }
        }
        function changePage(sTargetPage) {
            var frmPage = document.getElementById('iframeName');
            frmPage.src = sTargetPage;
        }
    </script>