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

in Ruby on Rails adding auto complete textbox is pretty simple. here is a simple example of it ...
in this example there will be 2 tables in DB. Customers table & Messages table. In the Customers table customer name and address will be saved. In the Messages table customer name and message to that customer will be saved. In the message form if we start typing the customer name, the name of the customers will be shown and we can select a particular customer name. that all. so lets start ...

Here i use Netbeans 6.0 as IDE

1. first create a new rails project.
2. run Rake Task to create the db
3. generate scaffold with this parameter in the [Model Name:] text field

Customer name:string address:text

4. run Migrate Database to create the customers table
5. now run this project
6. in the browser go to http://localhost:3000/customers and add some customers name and address
7. now generate another scaffold with this parameter in the [Model Name:] text field

Message to:string body:text

8. run Migrate Database to create the messages table
9. now the plugin Auto_complete have to be downloaded
10. download auto_complete plugins from github
11. unzip the downloaded zip folder and rename the folder 'auto_complete'
11. store 'auto_complete' folder in the "\vendor\plugins\" folder. [i.e. \vendor\plugins\auto_complete]
12. now, open the file 'messages.html.erb' from \app\views\layouts and add the following line before tag

<%= javascript_include_tag :defaults %>

13. now, open the file 'new.html.erb' from app\views\messages and change this line

<%= f.text_field :to %>

to

<%= text_field_with_auto_complete 'message', 'to',{}, :skip_style => false  %>

14. open MessageController and add this line

skip_before_filter :verify_authenticity_token, :only => [:auto_complete_for_message_to]

after this

class MessagesController < ApplicationController

15. add this new function in this controller:

def auto_complete_for_message_to()
user_name = params[:message][:to]
@customers = Customer.find(:all , :conditions=>"name like              '%"+user_name.downcase+"%'")
render :partial => 'username'
end

16. now create a new partial file in app\views\messages and name it _username.html.erb
17. paste this code in this partial file

<ul class="allusers"><% for customer in @customers do %><li class="thisuser"><div class="useremail"><%=h customer.name %></div><div class="username"><span class="informal"><%=h customer.address %></span></div></li><% end %></ul>

18. now restart server and in the browser go to http://localhost:3000/messages and now in the to field start typing u'll see some name coming from DB.
19. so its woking !!!!!!!!!!!!!!!!!!!!!!!!!!!

a. First, let's check to see if you already have Ruby installed. Bring up a command prompt and and type ruby -v. If Ruby responds, and if it shows a version number at or above 1.8.2 then type gem --version. If you don.t get an error, skip to step 3. Otherwise, we.ll install a fresh Ruby.
b. If Ruby is not installed, then download an installation package from rubyinstaller.rubyforge.org. Follow the download link, and run the resulting installer. This is an exe like ruby186-25.exe and will be installed in a single click. You may as well install everything . It's a very small package, and you'll get RubyGems as well alongwith this package. Please check Release Notes for more detail.
c. With RubyGems loaded, you can install all of Rails and its dependencies through the command line:

C:\> gem install rails --include-dependencies

Keeping Rails Up-to-Date:
Assuming you installed Rails using RubyGems, keeping up-to-date is relatively easy. Issue the following command:

C:\> gem update rails

This will automatically update your Rails installation. The next time you restart your application it will pick up this latest version of Rails. While giving this command, make sure you are connected to the internet.

Installation Verification
You can verify if everything is setup according to your requirements or not. Use the following command to create a demo project.

C:\> rails demo

This will generate a demo rail project, we will discuss about it later. Currently we have to check if envrionment is setup or not. Now next use the following command to run WEBrick web server on your machine.

C:\> cd demo
C:\demo> ruby script/server
=> Rails application started on http://0.0.0.0:3000
=> Ctrl-C to shutdown server; call with --help for options
[2007-02-26 09:16:43] INFO WEBrick 1.3.1
[2007-02-26 09:16:43] INFO ruby 1.8.2 (2004-08-24)...
[2007-02-26 09:16:43] INFO WEBrick::HTTPServer-start:pid=2836...
....

Now open your browser and type the following address text box.
http://localhost:3000