Update 2: This update goes here because circumstances have changed. If you missed the hype, Arstechnica.com has a great explanation of what happened. The download link still works for a select few, so feel free to try, but don't be surprised if it doesn't work any more. Read on for the original post and a short explanation...
In short, Adobe wanted to help those who still had valid, purchased CS2 licenses be able to still activate new installations (if they, say, changed computers or hard drives) after they had retired the CS2 activation server. For some reason, they chose to provide free access to these customers (and everyone, subsequently) to a new, downloadable version with serial numbers that would not require activation, but that would at least unlock the software -- all you needed to do was create or use your existing Adobe ID. After realizing their mistake, they briefly made another, removing the requirement to enter an Adobe ID altogether, before finally shutting down the links and redirecting those who visited them to the current CS6 site. As stated, Arstechnica has a more thorough explanation if you want to know more...
In an interesting move, Adobe has made the 2005 CS2 Premium Plus suite available as a free download for Windows and Mac platforms. While the software will have issues with some newer computers and though the software is dated, it's all here on Adobe's site, serial numbers and all. What do you guys make of this?
You do need an Adobe account to download the files, but it's completely free to create one...
[UPDATE] There is a lot of hype surrounding the free version of Adobe CS2. Many claimed it was false, etc etc. What's the story? Some people are reporting that the reason all this was happening is that Adobe is terminating the activation servers for CS2 and that for existing licensed users of CS2 who need to reinstall their software, copies of CS2 that don’t require activation but do require valid serial numbers were available.
But the downloads are free, and they still exist. There are serial numbers you can use, but there is a catch -- System requirements:
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
You should also be able to use Apple computers with newer Intel processors, but you have to have OSX v. 10.6.x or earlier (that's Snow Leopard or earlier...no Lion/Mountain Lion).
You might run into issues if you're using newer software/hardware. You can get to a whole slough of downloads and serial numbers for CS2 at Adobe.com.