I’m running CS 5 on a PC.
My color cettings for CMYK are Euroscale coated V2.
Sometimes I exchange information with a Mac Computer running CS2. I receive PDF files and some of the colors are not what to be expected.
For instance a a picture sent from the MAC as PDF file with the background color C 100%, M 75 %, Y 0%, K 0% is reproduced as 80,60,0,0 on my PC. (20% less)
I have to manually change it to 100,75,0,0
Do you have Color Management on both Windows and Macintosh set to Adobe ACE (Adobe Color Engine)? If you have any other setting such as Apple CMM (ColorSync) or Microsoft CMM on one or the other platform, you should expect some inconsistencies, unfortunately.
Also numerous changes and improvements have been made in Adobe color management since CS2. If you compare color management between platforms with the same version of the Creative Suite (or even with just recent versions of same) and you have the same color management engine specified, you should not see the anomalies you report.