where can i download a 30 day trial of photoshop cs4 or cs5?

What?! I was simply answering your question why someone would ever want to download such an old version (aside from doing research on older versions of Photoshop - which I can't see the OP here wanting to do), and I am not condoning that behaviour at all. As a matter of fact, the "tools" to crack older trials are riddled with malware and viruses.

The only reason I became aware of these practices years ago is because a small number of students of mine resort to this path, with the end result almost always ending in their laptops becoming bricked/impossibly slow to work with due to the malware, and that affects their work in class, obviously.

And seeing the wording of the OP's message sets off alarm bells, in my opinion.