Well, there is a "dirty" way to open it. Just rename the file extension to ".zip" (and confirm the dialog), and open it with Stuffit Expander. It doesn't work with Panther's built-in zip-extractor (BOMArchiveHelper) -- so don't double-click the file, but choose "Open with > Stuffit Expander" from the contextual menu (control-click on the file). I tested this with Stuffit Expander 7.0.3, but my guess is that you can use almost any version...
You can also use the command-line utility unzip in Terminal -- in that case, you don't even have to rename the file. A simple unzip thisfile.exe is enough to get things going. I believe this command comes with Panther, but I'm not sure. Either way, you can obtain it from the Fink package called "zip."

