To install PostgresSQL 9.1 on Ubuntu 10.04 with Chef

apt_postgresql_ppa.rb

# mycookbook/recipes/apt_postgresql_ppa.rb
#
# This recipe should add the sources for
# PostgreSQL 9.1 using the PPA available at:
# https://launchpad.net/~pitti/+archive/postgresql

apt_repository "postgresql" do
  uri "http://ppa.launchpad.net/pitti/postgresql/ubuntu"
  distribution node['lsb']['codename']
  components ["main"]
  keyserver "keyserver.ubuntu.com"
  key "8683D8A2"
  action :add
  notifies :run, resources(:execute => "apt-get update"), :immediately
end

pg_server.rb

# roles/pg_server.rb

name "pg_server"
description "a PostgreSQL server"
run_list(
  "recipe[mycookbook::apt_postgresql_ppa]",
  "recipe[postgresql::server]",
  "recipe[database]",
)
override_attributes(
  :postgresql => {
    :version => "9.1",
    :dir => "/etc/postgresql/9.1/main"  # IF you don't include this, chef tries to find 
  }                                     # postgresql config files in /etc/postgresql/8.4/main
)