I had trouble installing the three CS2 files that were listed in the list of products on the download page, but installing the separate parts of CS2 all of which are available separately as well (and all come with activation codes) worked fine; it just took me 40 or so minutes to install everything.
On Adobe's site, there is a message that says there's a restriction on the download and activations; i.e. only previous owners of the products can use the activations, though today this restriction appears to have been lifted.
On starting each product you are asked if you want to register them with Adobe. I went ahead just to make sure this was a genuine offer and was rewarded with an accounts page. As each product was booted up, I was given the option of registering them with Adobe. I did so and now I have all the products listed 'officially' in my adobe account under 'My Products'.
Do bear in mind that CS2 was released back in 2005/6, so is now several years old. That said, the only difference between the CS2 copy of Photoshop and the latest version is that several of the long winded processes are now automated. You can still do virtually everything with CS2 Photoshop (Photoshop v9) that you can do with the latest version.
Considering the programs cost thousands to buy (if you purchased the whole package), this deal is amazing. I remember wanting a copy of Adobe Premier to do my video editing, but there was no way I could justify buying a license. At the time it was one of the best video editing software's around, and cost around £1500.