From Aptana

Before installing Aptana RadRails you'll need Aptana Studio. We recommend using Aptana RadRails with the latest release of Aptana Studio.

After you update or download Aptana Studio:

• Studio 1.2.1 and later users: Add RadRails to Aptana Studio by following the instructions at Aptana > My Aptana: Plug-ins: Platforms)

If you are using earlier versions of Aptana Studio:

• Studio 1.2 users: Add RadRails to Aptana Studio by following the instructions at Help > My Aptana: Plug-ins: Platforms)
• Studio 1.1 and prior users: Add RadRails to Aptana Studio by following the Start Page instructions (Help > Aptana Studio Start Page...)

Note: Once Aptana RadRails is installed, Aptana Studio will prompt you to install future updates.