I successfully installed MySql x86_64 in Snow Leopard and Ruby and Ruby Gems seems to be installed properly:
$ which mysql
$ which ruby
$ which gem
Your MySQL connection id is 404
Server version: 5.1.37 MySQL Community Server (GPL)
$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [universal-darwin10.0]
$ gem -v
Unfortunatly I get an error installing mysql gem:
$ sudo gem update --system
$ sudo env ARCHFLAGS="-arch x86_64" gem install mysql -- --with-mysql-config=/usr/local/mysql/bin/mysql_config
Building native extensions. This could take a while...
ERROR: Error installing mysql:
ERROR: Failed to build gem native extension.
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb --with-mysql-config=/usr/local/mysql/bin/mysql_config
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/ruby.h
Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/mysql-2.8.1 for inspection.