I think you can still get a trial version of Photoshop CS2 here: http://www.adobe.com/support/downloads/product.jsp?platform=windows&product=39
If you want to look at other options, try the Gimp. It's a free (open source) editor that is similar to photoshop in some ways. http://www.gimp.org/
If you're running OS X, then you'll either need to install X Windows from the install CD that came with your Mac or you can try Seashore - based on the Gimp but a little more stripped down and built for Cocoa: http://seashore.sourceforge.net/index.php
The last two options are completely free while the first is just a trial - if it's still available. Personally, I'm a fan of open source software but I still prefer Photoshop and Aperture for image processing/editing.