You want a Minecraft server that you can use without purchasing Minecraft? So a cracked server? To make your server open to cracked clients, just edit the server.properties file and change "online-mode=true" to "online-mode=false".

To actually set up the server, you'll almost certainly want to use a Bukkit server instead of a vanilla server (especially if you are making this a cracked server, as you will need addtional security measures since people no longer need a paid account). [url=http://wiki.bukkit.org/Setting_up_a_server]Here is a good instruction guide for setting up Bukkit[/url].

Once you have a working Bukkit server, you'll want to add some plugins ([url=http://wiki.bukkit.org/Installing_Plugins]this guide[/url] can show you how to). If you are going to have a cracked server, then you'll definitely need [url=http://dev.bukkit.org/bukkit-plugins/authme-reloaded/]AuthMe[/url] installed. This forces all players to set a password and enter it when they log in (without it, someone could become admin just by setting their username to an admin's username). Note that AuthMe requires some advanced installation and you'll want to follow [url=http://dev.bukkit.org/server-mods/authme-reloaded/pages/how-to-install-and-initial-configuration/]their how-to guide[/url] to set it up. Other plugins I recommend:

--[url=http://dev.bukkit.org/bukkit-plugins/worldedit/]WorldEdit[/url] - allows large scale world editing
--[url=http://dev.bukkit.org/bukkit-plugins/commandbook/]CommandBook[/url] - adds tons of essential commands and functions, too many to list here (n.b. requires WorldEdit to be installed)
--[url=http://dev.bukkit.org/bukkit-plugins/worldguard/]WorldGuard[/url] - allows control of world settings, region protections, blaclisting items, etc (also requires WorldEdit to be installed)
--[url=http://dev.bukkit.org/bukkit-plugins/vanish/]VanishNoPacket[/url] - allows admins/mods to make themselves invisible to monitor for griefers
--[url=http://dev.bukkit.org/bukkit-plugins/nocheatplus/]NoCheatPlus[/url] - prevents all sorts of hacking
--[url=http://dev.bukkit.org/bukkit-plugins/permbukkit/]PermissionsBukkit[/url] - needed for managing permissions (more on that later)

Now you need to configure your plugins. WorldEdit, VanishNoPacket, and NoCheatPlus don't require much configuration (if any) so I'm not gonna bother linking to their config guides (you can find them with their respective links above). However, you'll definitely want to mess with the configuration files for CommandBook ([url=http://wiki.sk89q.com/wiki/CommandBook/Configuration]config guide here[/url]). You may also wish to edit the config for WorldGuard ([url=http://wiki.sk89q.com/wiki/WorldGuard/Configuration/Bukkit]config guide here[/url]) depending on your preference.

Now you'll need to configure permissions. Permissions means settings exactly what groups are allowed to do what (i.e. what commands, functions, etc they have access to). Each plugin defines so-called nodes, which usually look something like "pluginname.somecommand". Permissions are tricky, so [url=http://pastebin.com/raw.php?i=KGhaYFRJ]I made you a starter config file[/url] that should work well if you start with the plugins I listed (just copy that and paste it into /plugins/PermissionsBukkit/config.yml once you have installed the PermissionsBukkit plugin and run the server once). You may want to tweak it depending on what you want people to be able to do, and also if you add more plugins you'll need to setup permissions for those.

That should just about do it. Given that you already run some other servers, I assume you already know how to handle port forwarding and whatnot, so I'll leave that up to you.

This post was really long for a comment, but really brief for a Minecraft server setup guide, so if you have questions, feel free to message me here on Steam or reply to this comment. I'd be glad to help out with your server as much as I can. :D