Click Site Actions and on the Site Settings page in the Look and Feel section, click Tree view.

Select Enable Quick Launch to display the Quick Launch view, or select Enable Tree View to display a folder view.

As an example of a customization that you can make to left navigation, you can collapse Quick Launch and add fly-out menus to the view by setting attributes on the Menu control. This kind of customization requires that you either customize the originally installed default.master file through a SharePoint-compatible editing application such as Microsoft Office SharePoint Designer 2007, or that you create a custom .master file and use the Windows SharePoint Services object model to point a site to the new file.

Click Site Actions, click Site Settings, and then in the Galleries section of the Site Settings page, click Master pages.

On the Master Page Gallery page, click Edit in Microsoft Office SharePoint Designer on the drop-down menu.

In Code view, find the ContentPlaceHolder container control whose ID is PlaceHolderLeftNavBar. Within the PlaceHolderLeftNavBar control, find the AspMenu control whose ID is QuickLaunchMenu.

Set both the StaticDisplayLevels and MaximumDynamicDisplayLevels values of the Menu control to 1, as follows:

<asp:AspMenu
  id="QuickLaunchMenu"
  DataSourceId="QuickLaunchSiteMap"
  runat="server"
  Orientation="Vertical"
  StaticDisplayLevels="1"
  ItemWrap="true"
  MaximumDynamicDisplayLevels="1"
  StaticSubMenuIndent="0"
  SkipLinkText=""
>

Save the file and open a site page to see the results of your changes.

Copy the default.master file in the \12\TEMPLATE\GLOBAL folder and rename it, for example, myDefault.master.

Open your new myDefault.master file and find the ContentPlaceHolder container control whose ID is PlaceHolderLeftNavBar.

In the PlaceHolderLeftNavBar control, find the AspMenu control whose ID is QuickLaunchMenu, and then set both the StaticDisplayLevels and MaximumDynamicDisplayLevels values to 1, as follows:

<asp:AspMenu
  id="QuickLaunchMenu"
  DataSourceId="QuickLaunchSiteMap"
  runat="server"
  Orientation="Vertical"
  StaticDisplayLevels="1"
  ItemWrap="true"
  MaximumDynamicDisplayLevels="1"
  StaticSubMenuIndent="0"
  SkipLinkText=""
>

To upload your myDefault.master file to the Master Page Gallery, click Site Actions, click Site Settings, and in the Galleries section, click Master Pages. Click Upload on the Master Page Gallery page to browse to your myDefault.master file and upload it to the gallery.

Create a Web site in Microsoft Visual Studio and use the Microsoft.SharePoint.SPWeb.MasterUrl property to point the site to the custom .master file, as shown in the following example.

SPWeb oWebsite = SPContext.Current.Site.AllWebs["MyWebSite"];
oWebsite.MasterUrl = "/MyWebSite/_catalogs/masterpage/myDefault.master";
oWebsite.Update();
oWebsite.Dispose();

To run this example, you must add a Microsoft.SharePoint.WebControls.FormDigest control to the page that makes the post. For information about how to add a FormDigest control, see Security Validation and Making Posts to Update Data. The example also requires referencing and importing the Microsoft.SharePoint and Microsoft.SharePoint.WebControls namespaces. For basic information about how to create a Web application that runs in the context of Windows SharePoint Services, see How to: Create a Web Application in a SharePoint Web Site.

Reset IIS for your changes to take effect and navigate to a site page to see the results of your changes.