Short and sweet install script.

Installxbmc.sh

#!/bin/bash

  mkdir /home/setup
  cd /home/setup

  apt-get install pastebinit python-software-properties pkg-config -y

  usermod --group sudo,cdrom,audio,video,plugdev,fuse xbmc > /dev/null 2>&1
  adduser xbmc users > /dev/null 2>&1

  apt-get install xinit policykit-1 upower udisks acpi-support -y

  wget -q https://raw.github.com/uNiversaI/xbmc-ubuntu-minimal/master/12.04/download/custom-actions.pkla -O /var/lib/polkit-1/localauthority/50-local.d/custom-actions.pkla

  echo "usb-storage" | sudo tee -a /etc/modules > /dev/null 2>&1
  echo "xbmc             -       nice            -1" >> /etc/security/limits.conf && exit 0 > /dev/null 2>&1
  
  mv /etc/environment /etc/environment.bak
  echo "LC_MESSAGES=\"C\"" | sudo tee -a /etc/environment > /dev/null 2>&1
  echo "LC_ALL=\"en_EN.UTF-8\"" | sudo tee -a /etc/environment > /dev/null 2>&1

  apt-get install alsa-utils libasound2 -y
  amixer -q set Master 100% unmute 
  amixer -q set PCM 100% unmute
  amixer -q set 'IEC958',1 unmute
  alsactl store 0

  wget https://raw.github.com/uNiversaI/xbmc-ubuntu-minimal/master/12.04/download/remote_wakeup_rules -O /etc/udev/rules.d/90-enable-remote-wakeup.rules
  
  sudo ./gcs.sh upgrade && exit 0 > /dev/null 2>&1

  add-apt-repository ppa:ubuntu-x-swat/x-updates -y
  apt-get update
  apt-get install nvidia-current nvidia-settings libvdpau1 -y

  bash -c "echo allowed_users=anybody" >> /etc/X11/Xwrapper.config > /dev/null 2>&1 

  cp xorg.conf /etc/X11/xorg.conf
  apt-get install lm-sensors -y
  yes | sensors-detect
    
  mv /etc/sensors3.conf /etc/sensors3.conf.bak
  mv sensors3.conf /etc/sensors3.conf
  mv xbmc.conf /etc/init.xbmc.conf

  service apparmor stop > /dev/null &2>1
  service apparmor teardown > /dev/null &2>1
  update-rc.d -f apparmor remove > /dev/null &2>1
  apt-get remove --purge apparmor -y > /dev/null &2>1

  mv /etc/init/rsyslog.conf /etc/init/rsyslog.conf.bak
  wget https://raw.github.com/uNiversaI/xbmc-ubuntu-minimal/master/12.04/download/rsyslog.conf -O /etc/init/rsyslog.conf

  apt-get -y autoremove > /dev/null 2>&1
  apt-get -y autoclean > /dev/null 2>&1
  apt-get -y clean > /dev/null 2>&1
  apt-get -y install lirc