Right now you can get several Adobe computer programs for free for both windows and mac including photoshop cs2. just go to this link and click the download you want. http://www.adobe.com/downloads/cs2_downloads/index.html
the minimum system requirements for these are...

•Mac OS X v.10.2.8–v.10.3.8. PowerPC® G4 or G5 processor
•Microsoft® Windows® 2000/Windows XP. Intel® Pentium® III or 4 processor