Adobe are giving away Photoshop and CS2 free of charge - you have to register, but that's it. Right now the site is either snowed under or down, so it may be best to wait a day or two. Full details are here:

http://gizmodo.com/5973730/grab-photoshop-and-cs2-for-absolutely-free-right-here

The Mac version, incidentally, is for PowerPC chipsets, not Intel.

Sorry, someone messed up at Adobe, this turns out to be untrue, see:
http://www.diyphotography.net/download-adobe-cs2-for-free
for the true story

Well, this is weird - It's back on line, nobody seems to know what's going on, but I'm just installing Acrobat 8 for mac and it seems to be OK - I'm a legit user of the PC version so I won't feel guilty about this if it turns out to be another error. See

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

The general theory is that Adobe have decided that it's so old that they might as well give it away, but there has been no official announcement. It's safe to assume that there will be no support for this whatever!