[Javascript] switch/case what's wrong here?

[Richard]

www.somestuff.batcave.net/test1.html

Worked out most of the bugs on this monster.
Guess I need some fresh eyes to tell me what I've missed.
Switching from category to category works just fine.
When you click on a thumbnail, nothing happens.

Comments suggestions and other help appreciated.

thanks.

I've run it through the validator ok?
So I know about the alt tags.