i'm using Ubuntu 8.10. here is the steps how i install RoR in ubuntu. i get this instruction from Ubuntu Community documentation. I just mention here the steps that i do to install RoR.

1. at first open the terminal and to get Ruby run this command

sudo apt-get install ruby-full build-essential

this command also install a web server named 'WEBrick'

2. Now to download and install ruby gems we to run the following command one after another

wget http://rubyforge.org/frs/download.php/45905/rubygems-1.3.1.tgz
tar xzvf rubygems-1.3.1.tgz
cd rubygems-1.3.1
sudo ruby setup.rb
sudo ln -s /usr/bin/gem1.8 /usr/bin/gem
sudo gem update --system

this will install Rubygems 1.3.1

3. then we install RAILS as gem

sudo gem install rails

4. so, RoR is installed in Ubuntu.

5. now we will install MySQL database and it's connector

sudo apt-get install mysql-server mysql-client
sudo apt-get install libmysql-ruby libmysqlclient-dev
sudo gem install mysql

6. now to create a new rails application run this command

rails /home/www/test_app -d mysql

this will create a new applicaton named 'test_app' in '/home/www' directory

7. now to run the application do the following

$cd /home/www/test_app
$ruby script/server

then go to open the browser and go to 'http://0.0.0.0:3000'. new application will respond