server creation?

Q: is owning a server (tower I think its called?) illegal in residential areas?

A: If owning a computer is illegal for you, then yes, owning a server is illegal. Otherwise, you should be fine in terms of law. Your ISP might not like you hosting servers, but they won't know you are unless you're getting very high traffic to your IP address. If you're just using it for yourself and a couple friends, you should be fine. If you're running it for a lot of traffic, clear it with your ISP first.

Q: can servers be bought prebuilt? or do they HAVE to be hand built (I'm not good with building PC's XD so this could prove a problem)

A: Yes, they can be bought pre-built. They are usually quite expensive though because they're usually designed appropriately. They can also have extra features built in that you don't normally find equipped on a regular PC. You don't have to build one, though. An old computer, separate computer, or virtual machine can be used instead, and should cover most cases.

Q: are they hard to maintain?

A: Depends on your usage and operating system. I can't really give a definitive answer here, but I can at least say that you can't leave your server to rot if you want to use it often. Keep it in top shape as best you can. It is recommended that you use an operating system that is light, but secure. Graphical user interfaces should not be used, especially if it's a PC turned into a server or if you're using a virtual machine. Also, keep in mind electricity bills if you want to keep the server running 24/7.

Q: what all would I need to run one?

A: A computer and an operating system of your choice, really. Of course, that's simplifying the matter. If you need more than one node, you better study up on networking.

Q: can they be stacked on top of each other, or do you NEED the tower to prevent things like overheating/throttling and all that.

A: You don't NEED the racks if you only have one or two of them. Racks help with organizing the servers (as well as managing their cords for network switches), but you won't need them if your server(s) are minimal.

Q: is there anything specific they need for running game servers?

A: Proper software and enough CPU power to handle all the requests and serving of all the clients. Honestly, you don't really have to worry about CPU power unless you plan on having MANY people connect.

PS: Keep in mind that you're going to need some knowledge before setting one up. Buying a pre-built server doesn't automatically mean you'll get your server up and running in a flash. And once you've set it up, keep it to just you and a couple friends for awhile, so you can get a feel for how it runs.

A "Server" is a function or style of use rather than any physical style of machine.

You have "server" programs on your normal PC as part of the operating system; software that takes and responds to requests from other pieces of software.

Server and Client are just ways of describing classes of functionality.

(Companies like internet hosts use slimline rack-mount computer enclosures just so they can pack masses of machines into a small space)

Any moderate specification, general PC system can be used to run game servers.

They do not need fancy hardware or GPUs and for a single game with a few users, they do not need to be as powerful a machine to actually play that game.

The essential thing is an Ethernet connection, plus a good internet connection with correct port forwarding set up to the server machine so other players can join the game on the server.

A surplus desktop that someone considers too slow for general use would be fine for many things.

Do a clean re-install of the operating system, with a full format of the drive(s) to get rid of junk and any nasties etc. then install the game & run in server mode.

I've always used Linux (Centos) for servers, as it takes less CPU load just to run the system and all the games I've been interested in playing multi-player have had linux support.

Windows will work but is rather less stable and will tend to load the CPU more.

My company builds small business servers; we normally use general PC cases, particularly the Antec P280 as it has good airflow and works fine for servers, gaming machines, CAD systems etc.

The servers are only ever Linux based as we don't want the hassle of breakdowns and software problems etc.

A properly built machine will generally run for ten years or so without hassle.

you can use ANY machine as a server anywhere you like.