Ruby setup on mac

I followed the setup instructions on hivelogic website for installing
ruby on mac leopard. The trouble I am having now is that the default
db is sqlite rather than mysql. I don't know how to change my ruby
config from sqlite to mysql. Can someone point me in the right
direction?

rails -d mysql your_app_name

Is this for a new or existing project?

This is for a new project.
You only need to change database.yml if you have an existing project.

Refer to:
http://weblog.rubyonrails.org/2007/12/17/rails-2-0-2-some-new-defaults-and-a-few-fixes

By the way, why did you install Ruby from Hivelogic on Leopard. Mac OS
X Leopard comes with Ruby built right in. It's what I use and I've
seen no problems using it. It's find, but I was just curious.