Microsoft have made available an update for Windows Server 2008 that integrates the WSUS 3.0 console into Server Manager.
By default, Windows Server 2008 includes several server roles. Server Manager enables integration of additional roles and features that are available from the Microsoft Download Center and from Windows Update Web sites as optional updates to Windows Server 2008. One role that is available as an update is Windows Server Update Services (WSUS) 3.0 with Service Pack 1 (SP1). This update for Server Manager in Windows Server 2008 fully integrates WSUS 3.0 SP1 into Server Manager. This update lets you use the Server Manager snap-in and wizards to install, configure, and manage WSUS 3.0 SP1.
You can read about the update via the knowledge base article and then download the update for Windows Server 2008 32-bit or Windows Server 2008 64-bit.