Alas, it simply is not installed by default - to install it, you need to add a Windows Feature (via Server Manager) and add Desktop Experience. Enable that (it will require the 'Ink' feature as well) and reboot. However, it won't show up as a friendly icon - to access it, open a new command window (run as Administrator) and enter cleanmgr.exe then hit return.
FYI: Why would you do this? Well W2008 hides most of the files it uses for updates, etc. and they cannot be deleted. This means you end up with a lot of junk on the server no matter how much you try to clean up. Case in point: Last SharePoint server I cleaned up - 3.6GB of junk removed BTW - if you are worried about overhead, particularly with SharePoint - worry not! It has to be enabled for PowerPoint libraries to work anyway (that's another post here)!