Assuming you’ve followed the Hivelogic article that walks you through a basic Ruby on Rails installation, you can use this code snippet to install Ruby 1.8.6.
curl -O ftp://ftp.ruby-lang.org/pub/ruby/1.8/ruby-1.8.6.tar.gz
tar -zxvf ruby-1.8.6.tar.gz
./configure --prefix=/usr/local --enable-pthread --with-readline-dir=/usr/local
sudo make install
sudo make install-doc
sudo gem install rails --include-dependencies
Windows users only need to snag the latest version of Curt Hibbs’ One Click Ruby Installer which can be downloaded here.
The major advantage of moving to Ruby 1.8.6 and Rails 1.2.3 is that breakpointer works again.
Update: When I did this on my Macbook Pro, I had to recompile a few libraries like Ruby-DBI and Ruby-ODBC before I could connect to Microsoft SQL Server again.