I installed everything from source on Ubuntu and it wasn't difficult,
but I found that it was easier to use MacPorts to install MySQL, Ruby
and RubyGems and then use RubyGems to install all the gems you want.
I have written a <a href="http://blog.rayvinly.com/articles/2007/11/29/
setting-up-ruby-on-rails-with-mysql-on-mac-os-x-10-5-leopard">blog
post</a> about how I got it to work. Give it a try.