Using multiple Ruby versions

Is there a way to setup multiple versions of Ruby to use with
different projects like we can with the version of Rails? On my dev
machine I have Ruby 1.8.6 with Rails 1.2.3, which works fine. But one
of my projects uses Rails 1.2.2, which turns out to have problem with
Ruby 1.8.6. Instead, Ruby 1.8.5 is required. Is there a way to have
both versions of Ruby installed, and specify which one a project uses?


I wrote a blog entry last night on using multiple versions of Ruby:

I don't know how to easily specify which version a project should use
and have it automatically switch though.