Ruby on Rails on Ubuntu

Today, I installed ruby on rails on my Gutsy-Gibbon (Ubuntu 7.10) OS. I followed these steps (which I swiped from an excellent posting by Walter Wilfinger):

sudo apt-get install ruby rdoc irb libyaml-ruby libzlib-ruby ri libopenssl-ruby
wget http://rubyforge.org/frs/download.php/29548/rubygems-1.0.1.tgz
tar xzvf rubygems-1.0.1.tgz
cd rubygems-1.0.1
sudo ruby setup.rb
sudo ln -s /usr/bin/gem1.8 /usr/bin/gem
sudo gem update --system
sudo gem install rails
sudo apt-get install build-essential ruby1.8-dev
sudo gem install mongrel
sudo apt-get install mysql-client mysql-admin mysql-query-browser libmysqlclient15-dev
sudo gem install mysql
sudo apt-get install sqlite3 swig libsqlite3-ruby libsqlite3-dev
sudo gem install sqlite3-ruby
echo "export RUBYOPT=rubygems" >> ~/.profile
rails path/to/your/app

but I got stuck at

sudo apt-get install build-essential ruby1.8-dev

The terminal asked me to put the Ubuntu install disk in the CDROM drive.

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UPDATE: I realized that the above step (upon which I was “stuck”) was unnecessary. I just skipped down to the mysql lines.