I think there should be unsubscribe link at the end of one of those messages you get...or you can probably do it from the Beyond Pet Talk page too...

Here's how to leave the group:
1. Go to http://groups.yahoo.com/group/beyondpettalk/ and sign in if you're not already signed in.

2. Click Edit My Membership in the top right hand corner underneath the Start a Group, My Groups, and Sign Out links.

3. Scroll to the bottom of the page and click on the Leave Group button.