Get an image: http://www.raspberrypi.org/downloads
Put it on your SD card. Good instructions for OSX or Unix: http://ryanphilipsullivan.blogspot.com/2012/06/raspberry-pi-getting-started-with.html
Log in as username: root, password: root.
You should be able to do a full system upgrade with:
pacman -Syu
If you want to change mirrors, just edit this file:
/etc/pacman.d/mirrorlist
Optionally, add a non-root user (in this example, the user is named 'dev')
useradd -m dev
passwd dev
Install some packages:
# util
pacman -S alsa-utils alsa-firmware alsa-lib alsa-plugins
pacman -S autofs
pacman -S sudo
pacman -S zip
pacman -S rsync
pacman -S unzip
# dev
pacman -S gcc
pacman -S make
pacman -S git
pacman -S nodejs
pacman -S apache
pacman -S python
pacman -S python2 # older python, required by some packages
In order to install Tahoe FS, install python 2.x, then download and expand Tahoe. In the Tahoe dir:
python2 setup.py
Restart Apache in Arch Linux issue the following command:
/etc/rc.d/httpd restart