The easy way, take any old machine you have and load Linux Server on it. Ubuntu server is also easy. All a server (in the true sense) is a heavy duty machine with server software loaded on it.
Here are some good guides to building the "perfect" server.
http://www.howtoforge.com/perfect_setup_…or
http://www.howtoforge.com/perfect-server…or
http://www.howtoforge.org/perfect-server…Those really are easy to follow guides and do setup an easy to use webserver with email, ftp , etc.
Real servers usually are "beefed up" computers and have lots of hard drive space with fast raided HDs and plenty of ram, many have two or more processors with redundant power supplies. However, they still are just computers.
