Well it's not what the 'Desktop PC' can do; it's the operating system. It depends what operating system you are currently running, and what version, particularly when talking about Windows. If you're running Windows 7 Professional you're on an 'interim' version between a basic operating system and a server based system.
In a nutshell, Windows Server 2008 could host various services. Host is the important term, here. If you integrate Windows Server with Terminal Server you could run say five (for instance) users from one machine and allow access to all of the server's resources via Remote Desktop - the client is available from most versions of Windows.
Furthermore you could install 'IIS' - Internet Information Services, which is Microsoft's version of a 'web server'. I am not familiar with IIS, so unsure of it's exact features and capabilities but the upshot is that you could host your own website from server.
There are many more features of Windows Server, but I thought I'd just list a couple of simple features. Hope this helps.
answered Jul 25 '10 at 08:50