How to set up your Minecraft so you can play on the Xanadu server:

1. Download the XanaduClientSetup.zip from http://www.ratbastards.org/downloads/CompleteSetup/XanaduClientSetup.zip and extract the contents.
2. Copy "Magic Launcher" to your Applications Directory
3. In the Finder, select "Go > Go to Folder..."
4. Enter "~/Library/Application Support/minecraft" as the path of the folder to go to.
5. From the "XanaduClientSetup/bin" directory copy the file "minecraft_1.5.1.jar" to your "minecraft/bin" directory.
6. From the "XanaduClientSetup" directory copy the "mods","coremods" and "magic" folder to your "minecraft" directory. (NOTE: If any of these directories already exist, do not replace them, but instead add to the existing folders with the contents of the folders extracted from the setup archive.)
7. From the "XanadaClientSetup/config" directory copy the folder "railcraft" to your "minecraft/config" directory. If the directory doesn't exist, create it. 
8. Launch the "Magic Launcher" application.
9. Click the "Setup" button.
10. Click the "New" button and enter "Xanadu" as the name of the configuration, copying from "Default". Click the "OK" button.
11. Click the "Select" button and choose "minecraft_1.5.2.jar"
12. Click the "Add" button and select "minecraftforge-universal-1.5.2-7.8.0.715.zip" in your minecraft/magic directory. There will be 1 error which can be ignored.
13. Click the "Add" button and select "[1.5.2]ReiMinimap_v3.3_06.zip" in your minecraft/magic directory.
14. Click "OK" to close the setup screen.
15. Enter your Minecraft log in information and click "Login". Minecraft will launch after a brief setup phase.
16. Click "Multiplayer" and set up the Xanadu server: xanadu.ratbastards.org:25765.

You are now ready to join!

To play vanilla minecraft, select "Default" from the configuration menu when you start Magic Launcher. Magic Launcher disabled the Minecraft update prompt, so to get new versions of Minecraft, launch the regular Minecraft application. Or you can just launch the Minecraft application directly to play vanilla.