A new version of the Arduino can be downloaded from the Arduino website.
After downloading it can be unpacked anywhere, and it should run out of the box (tested August 8 2013 with Uno R3, December 25 2015 with USB).
For more information see the Debian entry in Playground.
IMPORTANT NOTE: The "Arduino IDE" package in the Ubuntu 10.10 (Maverick) repository is version 18 and does not support the latest Arduino UNO, see below.
the Ubuntu repositories are a long way behind, so the default package in Maverick does not support those boards.
Version 0018 of the IDE is from January 2010, the Uno and Mega2560 were released in September/October 2010.
To install, you have to enable the maverick-backports repository in the "Ubuntu Software Center" settings or do the following: Alternatively, you can use: Easy walkthrough with lots of screen shots of the official IDE from the main Arduino site. The repository version 0018 does not work with these later boards.