To be honest: No, you cannot get much done with that, as far as a game server is concerned.
From the little research I did looks like its a P3 CPU, limited SD ram, and with 18gb of storage you might get one or two maybe games installed after O/S.
So a game server is very limited, maybe a server for older games, but really isn't made as a game server anyway.
You could fit in a larger HDD and would be a great file server, and rackmounted servers you can typically hide away pretty easy, and use somewhat limited power.
But also depends on your home connection/friends with fast connection hookup. I had a friend who had a friend who worked at a local ISP and we gave him a old computer of ours. I used this back in Beta1 and also in CS:S. It was pretty dang good server since it had a near dedicated T3 line running to it.
So if you can get the internet for it, then might be a not bad choice for a file server.