如何在Aptana RadRails中使用旧版本的Rails？

I'm new to Rails development, and I'm trying to figure out how to use an older version of Rails with Apatana's RadRails IDE. I'm trying to help out a friend who has a site built on older version than the one that automatically gets downloaded by RadRails, and I'm pretty sure the two versions wouldn't be compatible (the site is using some pre 2.0 version, not sure of the exact number offhand).I'm new to Rails development, and I'm trying to