Depends on which Operating system you are running. If Windows XP or older, CS2 should be fine. It may not like Vista/7. If on a Mac, CS2 is likely to not work on an intel mac, particularly with the later OS (Snow Leopard and later).
There's nothing wrong with GIMP... really. If you want to update to something more recent, and are unwilling to "acquire" a leter version of photoshop, maybe look at Photoshop elements which is a perfectly acceptable alternative to the full program (and arguably, probably better than the full program for those of us who are not professionals). Its much cheaper, and has most of the important bits you'd be wanting. However, for general photo management and editing it might be worth taking a look at Lightroom, too. Again, this is cheaper than Photoshop, and for many of us, has replaced it almost completely.