Adobe, developer of tools like Photoshop and many others, offers old version of their application usable for Mac and Windows for free.
Those are, for example, Creative Suite 2, Acrobat 3D, Acrobat Standard 7, Acrobat Pro 8 and Photoshop CS2.
They provide free serial numbers, no registration necessary.
http://www.adobe.com/downloads/cs2_downloads/index.html