A non-arts-related friend pointed this out to me - free downloads of CS2 products. I'm assuming they don't work too well on newer operating systems (otherwise Adobe wouldn't hand them out) but if you have an older computer...?

http://www.adobe.com/downloads/cs2_downloads/index.html

Seems a bit odd, but there you go.

Edit: Apparently CS2 works fine with Win7 64bit. Even better.

From Adobe:

"Effective December 13, Adobe disabled the activation server for CS2 products and Acrobat 7 because of a technical glitch. These products were released over 7 years ago and do not run on many modern operating systems. But to ensure that any customers activating those old versions can continue to use their software, we issued a serial number directly to those customers.  While this might be interpreted as Adobe giving away software for free, we did it to help our customers".

They have finally updated the page to point out that these files are only for existing CS2 license holders:

Adobe has disabled the activation server for CS2 products, including Acrobat 7, because of a technical issue. These products were released more than seven years ago, do not run on many modern operating systems, and are no longer supported.

Adobe strongly advises against running unsupported and outdated software. The serial numbers below should only be used by customers who legitimately purchased CS2 or Acrobat 7 and need to maintain their current use of these products.

Use this link to install on windows 7 64bit.  it works

 http://planetmediocrity.com/2013/01/installing-photoshop-cs2-on-windows-7-64-bit/