I’m supposing you placed the file WordService.service it on ~/Library/Services (~ = your user’s folder).
Other than that, you’ll have to go to System Preferences > Keyboard Preferences Pane > Services and check-in the services that you want to be available (there will be many, from different apps, so you’ll have to track down the ones from WordService that you want to use). You can also assign them shortcuts.
Make sure that you logout or restart the computer after that.
Then, you will have to select any text on any cocoa application, choose the service to use (via menubar or shortcut) and voilá!.
Macworld has a nice article about how Services work under Snow Leopard.
Best,
– MJ