The PC link points to an executable file, which is an install program. Executing it will install the software on the client's PC.
The Mac link is a zip file, which has special instructions for installing the software: 1. In Safari go to the Safari menu and choose preferences.
2. Under the general tab Uncheck the section that says "Open "safe" files after downloading"
3. Then redownload the Mac software.
4. This should put a zip archive where you're downloading to.
5. Double clicking it should unpack the zip file providing you with an application instead of the contents folder that you're probably getting now.
Minimum system requirements for the software: PC: Microsoft Windows 2000 or Later with Java 1.5 or more Installed. Mac: Mac OSX 10.4 (Tiger) or Later with Java 1.5 or more Installed.