Ok, lemme get a crack at this.
I assume that you are downloading the files off the forums. For some reason, sometimes it downloads as "attachment.php" for me. all I have to do is rename it "attachment.zip" (it doesn't have to be "attachment.zip", it can be "anything.zip"). Then, it just opens in Stuffit Expander. Since yours download as just attachment, attachment 1, etc, I assume you have hide all extensions enabled. Just "File-> Get Info" and go down to "Name and Extension," and change the extension to .zip. Try that. And please, stop the wall-bashing.