OK, you must understand that the word server, in the loosest terms, means a computer that hosts a file or resource and is accessed by other computers. Therefore, there is no set requirement, hardware-wise, for what a server must have.
So you could buy that thing, but is it really necessary? Unless you're going to be hosting like 100+ players at the same time, it really isn't. Get some A64, about a gig or two of RAM, and stick it with a good internet connection and that will do.
And yes, you'll need a server (or something that acts as a CS:S server) if you want to host CS:S games.