Gathering the Programs
___________________________________________________
Beta:  Go to http://www.minecraft.net/ and click Download under Beta, and download Minecraft.exe/jar/app and put it on your desktop.  Then, download Minecraft_Server.exe/jar and place it in a special folder on your desktop.

Classic:  Go to Multiplayer under Classic, and Download the server software.  extract the .zip file to your desktop.

Beginning Setup
___________________________________________________

First, go to http://portforward.com/
Then, select your router
Skip Advertisement (at top-right corner of screen)
Crtl-F (Press Control and F at same time) and type in Minecraft Server
Follow the instructions they give you.

[tip:  you need to go to your command promt/terminal and type in ipconfig /all in windows, and ifconfig in linux and possibly mac(?) for some information that you might need to port forwarding]

Further setup with Windows
__________________________________________________

Go to your control panel and go to Windows Firewall (or something like that) and create new port exception.  Create an exception for Port 25565, TCP.  Do the same with Minecraft.exe and Minecraft_Server.exe.  For the application name/application tab, put a note to yourself.  The entry name, isn't important to the program, but it is important [possibly] to you.  Just put something like Minecraft Classic or Minecraft Beta.

Note:  Make sure you dont have Dont allow exceptions box checkmarked. Un-checkmark that, and also DO NOT disable your entire firewall, as that WILL give viruses an invitation.

Go into your Antivirus program and make an exception for both Minecraft.exe and port 25565 (it varies with your antivirus on how to do this.  (Be sure to create a complete exception with this.)  Create an exception in the same fashion with Minecraft_Server.exe

[optional] set up a Static IP Address.

Further setup with Linux/Mac
___________________________________________________

There is no further setup, but its optional to setup a Static IP Address.

Going to the games:
___________________________________________________
In Both, go to your special folder containing your server software that you downloaded earlier, and start your server software once.  It will error out alot, but that's because it is creating files.  Exit out of your server software once it's done erroring out.  there will be alot of files in your folder now.  Now, go into server.properties, and open with notepad/gedit/whatever mac has and change your settings to whatever you want. JUST BE SURE TO KEEP YOUR PORT 25565, AND KEEP YOUR IP ADDRESS BLANK [ip address = ] but without the brackets.

Done.  Now, for
-Classic users, give people whatever is in your externalurl.txt file, so people can go on your server.

-Beta users, go to http://www.cmyip.com/ and give people that set of blue numbers [your IP Address] to everyone.  To get on your server, just enter in those blue numbers once you click on multiplayer in Minecraft.exe/jar/app

[Note:  If you did not set up a Static IP Address, then you have to constantly check your externalurl.txt for changes, and give people that new url, and you have to go to cmyip.com often to check if your ip address did not change, and give people your new ip address for people to go on your server.]