What you want to do is set up two appenders. Make one of them be the default appender for the root category.

Make another category for your 'special' class. Categories typically have the same name as the fully-qualified classname of the class in which they're used, so just mention that category in the config file. Make sure that the special category points to another appender that goes to the file that you want.

The trick is to set the additivity of the special category to false. This makes the difference between log messages that go to both files, and those that go to just one file.

Hope that helps,

-chris