As of this writing, the current Ubuntu version is Gutsy Gibbon, 7.10
Ubuntu Server Edition provides a server set up right out of the box. It is perfect for anything from sandboxing on an old PC, to full blown servers.
Option 1: Manual Setup
If using the Desktop Edition you will need to install the packages for Apache2, MySQL and PHP using either Synaptic or from the command line with apt-get. Here is a link to the Ubuntu documentation tutorial on How to setup an Ubuntu LAMP Server on a desktop edition.
Once the server is set up, to install Drupal you need to untar the contents of the Latest stable release to your /var/www directory.
There is also a video in the video and slides section which covers installation and getting clean URLs working.
Option 2: Automatic Setup using Synaptic Package Manager
This option is extremely easy if you have already configured postifix on Ubuntu (for email) - but is quick setup for a Drupal5 LAMP install even if you haven't configured postfix. (I haven't tested without postfix configured)
Using Synaptic Package Manger (Ubuntu: "Applications > System > Synaptic Package Manager"), select "Drupal5" package (from multiverse repository). This package will install any required modules needed to setup a working Drupal5 installation... such as Apache2, MySQL, PHP5, php-gd, and curl.
Drupal 5 Caution
Make sure you select apache2 when going throught the wizard. Navigate to localhost/drupal5 to see drupal admin console.
If you get bunch of MySQL errors that basicaly tell you that tables are not found, try