Nisus Thesaurus 1.0.6 brought back Services functionality for users on Snow Leopard. Unfortunately, it didn’t quite work for everyone. So, if you are one of those that doesn’t have Services functionality, Nisus Thesaurus 1.0.7 is for you. This release should work anywhere it is supposed to.
You can download Nisus Thesaurus 1.0.7 from the Nisus Thesaurus page.