1. Download the launcher from the following link (right click it and select "Save link as..."): site.eris.scalacubes.org/PlanetErisLaunch.jar
2. Make a folder and put the launcher in it.
3. Double-click to start the launcher.
4. Double-click "Eris Modpack" in the left pane.
5. Enter your Minecraft login information in the pop-up window.
6. The launcher will install all of the mods; it may take a little while. When it's done, Minecraft will start. Click on the "Multiplayer" button.
7. Click on the "Add Server" button.
8. Enter the name and address (18.104.22.168:2074) of the server and click "Done."
9. Double-click on the Planet Eris server listing.
10. Enjoy yourself! After this, just click on the launcher .jar and click on "Eris Modpack" every time you want to play. The mods are already downloaded, so subsequent logins will not take very long.