First you'll need to setup Craftbukkit.
Windows:

First, you will need to get Craftbukkit (if you're looking for a commonly used .jar)
1. Download CraftBukkit: [ Register or Signin to view external links. ]
2. Put the .jar file in the directory you'd like the server to run from
3. Open a text editor such as Notepad and type:

Note: 1024M = 1GB, 2048M = 2GB, 3072M = 3GB, 4096M = 4GB, 5120M = 5GB, 6144M = 6GB, and on and on and on.
4. Save the document as run.bat (not as a .txt) in the same directory as craftbukkit.jar
5. Double click run.bat and you're away!
6. To shut down, issue the "stop" command in console.
Source: Craftbukkit Wiki

Mac OS X

1. Install Java
Since OS X 10.7 Java does not come packaged with OS X. You will need to install java from the Apple's website [ Register or Signin to view external links. ]
2. Obtaining the Server Files
To run a server you will need the server jars, i.e. the server files. We will need a place to put the files.
1. Create a New Folder
Open up finder, and create a new folder in your Home folder named CraftBukkit
2. Download the File
Download the server files. You can download the latest builds from the front page of the wiki.
Note: Download the stable build if you are not chasing the cutting edge in the development build
3. Move the File
Move the file from the Downloads folder to the CraftBukkit folder you created.
3. Obtaining startup script
To easily start the server you will need a startup script. The following is a basic server script to start your server.
1. Open up TextEdit set it to plain text mode under format and paste the following in

2. Save the file
Save it in your CraftBukkit folder as start_server.command
3. Allow the script to run
1. Open up Terminal.app
2. Type into Terminal.app

Warning: Do not hit return
3. drag the start_server.command into Terminal.app
4. hit return
4. Starting the server
From this point on you can start the server by double-clicking start_server.command.
You will need to run the server once for it to generate some configuration files.
Warning: To stop the server, do not close the terminal/command prompt window. Instead, type 'stop' into the console. Closing the terminal window without stopping the server could lead to corruption of the save files.
Source: Craftbukkit Wiki

Port-Forward:

Note: This is a little different from router-to-router,your setup may be a little different. Go to your routers options page by entering (usually by default) 192.168.1.1 into the address bar, enter your username and password (the password is usually admin, also by default) once there, select Applications and Gaming.

Then go to Port Range Forwarding. This is where you select which ports you wish to forward, the default Minecraft server port is 25565, though it can be anything, I recommend it as a starting point. Anyway, enter an app name (something that tells you what it's for) and the ports you want forwarded (25565-25565) and then the protocol, Minecraft requires TCP and UDP so remember to do one for each, if you have an option in the drop-down menu that says Both then that will save you some typing. However, sometimes it does not work, and you will have to make a rule for each.

This is if you want Craftbukkit, if you want something else PM me.