久々にRailsプラグインの紹介です。

Plugins - NamedScope

This is not simple hack of named scope like you might find in WillPaginate. This is a fully backported and tested version of NamedScope that will work on rails 1.2.6 or 2.0.4.

Rails-2.0.4およびRails-1.2.6でNamedScopeが使えるようになるようです。