In the past I've blogged about one way to localize your web parts using really cool and surprisingly simple ASP.NET 2.0 localization techniques.
Today I stumbled across an old but extremely thorough post on the same subject by Mikhail Dikov; Mikhail's approach deploys .resx files directly to the file system instead of satellite assemblies and lets the platform handle the bulk of the work involved--until you've stepped in to create a custom job definition.
While my solution isn't necessarily the correct SharePoint way of handling resources I still think it's beautiful in its simplicity and will be familiar to any ASP.NET developer crossing the line into WSS/MOSS. The application of my suggested approach will depend somewhat on your solution structure but I'll always believe less code to build and maintain is a good thing.
Custom-Built Microsoft Office SharePoint Server 2007 Branded Sites and Webpart Development - firstname.lastname@example.org