I'd reinstall it. Just moving it might not correct file pointers needed to run the expansion.
It won't. Essential game data is stored in the registry, which I absolutely would
not recommend editing without knowing exactly what you're doing.
Definitely reinstall Pets, Ezuu. And welcome to the forum.
Also, would you mind modifying the title of this thread to be a little more descriptive? "Just a really quick question" does not help anyone just casually browsing the forum to know what this thread is about. You can do this by clicking the Modify button in the top right hand corner of your post.
Thanks.