Almost all discussions of Use Cases and UC templates eventually lead to Cockburns work. He makes some templates available in various formats on
http://www.usecases.org . I usually use a template based around this, but prefer something a bit lighter.
I would emphasise that the real value of use cases is in the boring stuff - the text, the steps, the paragraphs. A template can be useful (especially to remind you of missing information), but it should not be the focus. I would not spend too long working on a template or even a use case model. Start writing the use cases, and get a clear idea of the system you will be building.
regards,
paul.