Adobe is giving away the Creative Suite 2 bundle for free including Photoshop CS2. The latest version of Creative Suite is version 6 but you can't complain when you are getting it for free! 
Go to the Download page, register for a free Adobe account and download the three disc version of Adobe CS2 for Windows or Mac. The serial number is listed on the same page.
No body knows for how much time it will be available so if you are interested, head over there right now, download the files and copy the serial number.
Adobe provides direct download link and serial keys for the following software:
· Creative Suite 2 (Windows and Mac)
· Acrobat 3D 1.0 for Windows
· Acrobat Standard 7.0 (Windows and Mac)
· Acrobat Pro 8 (Windows and Mac)
· Audiotion 3 (Windows)
· Illustrator CS2 (Windows and Mac)
· InCopy CS2 (Windows and Mac)
· InDesign CS2 (Windows and Mac)
· Photoshop CS (Windows and Mac)
· Photoshop Elements 4.0/5.0 (Windows and Mac)
· Adobe Premiere Pro 2.0 (Windows)
Go to the official download page.