Using Rails 3? Thinking Sphinx 2 (currently a prerelease) supports Rails 3 only - here’s the lowdown on how to get it set up.
A concise and easy-to-use Ruby library that connects ActiveRecord to the Sphinx search daemon, managing configuration and searching.
Sphinx is a very fast search engine that indexes data and provides flexible ways of searching it. Thinking Sphinx allows you to link up your models into Sphinx simply and painlessly -– because let’s face it, searching across multiple fields using SQL is a pain in the neck.
Most importantly: How?
Read the quickstart guide, along with the rest of the documentation.
And when you get stuck, there’s always the google group.