from http://blogs.technet.com/wsus/archive/2009/05/12/installing-wsus-3-0-sp1-through-windows-server-2008-sp2-server-manager.aspx we read:
By default, Windows Server 2008 SP2 includes the ability to install the Windows Server Update Services Role Service by using Server Manager. This role lets you use the MMC Server Manager snap-in and wizards to install, configure, and manage WSUS 3.0 SP1. This behavior is different from Windows Server 2008 SP1 where the administrator needed to install an update to Server Manager to be able to install WSUS as a Role.
There is no need to install "Update for Windows Server 2008 Server Manager" (KB940518). This update is only applicable to Windows Server 2008 SP1 computers.
To install WSUS 3.0 SP1 on a Windows 2008 Server SP2 server that is pointed to Windows Update or Microsoft Update, go directly to Server Manager and install the WSUS Role.
To install WSUS 3.0 SP1 on a server running Windows Server 2008 SP2 which is being updated by a WSUS server, do the following procedure.
* Enable the following Product Classifications:
* Enable the following Category:
- Windows Server 2008 Server Manager – Windows Server Update Services (WSUS) Dynamic Installer category is a container for WSUS updates. These updates are “hidden” such that user will never see a notification or be downloaded by WUA. These updates can only be downloaded via the WUA APIs. Server Manager is using this method to download and start the install of WSUS.
* Approve the Windows Server Update Services 3.0 SP1 Dynamic Install for Windows Server 2008 (KB948014) (there’s one for x86 and one for x64). This specific WSUS package is targeted at Windows Server 2008 computers that do not have WSUS installed. This package will only install via Server Manager.
Note: Since the update is targeted at any Windows Server 2008 computers that don’t have the WSUS role installed, these machines will report that the update “is needed”. You do not have to install this update on these computers if you do not want it.
After WSUS is detected as installed by Server Manager it can be configured and managed within the Server
Manager UI/WSUS Snap-in.