iIf you last used PS7 and were OK with that I would really suggest you buy, or at least take a trial, of Photoshop Elements.  Believe latest is version 10.  It is only $100 so a lot cheaper than Photoshop and the learning curve not as steep.

It will probably have more features than your old PS7, and should run just fine on an older machine.

Buying a legitimate version of CS2 may be difficult for the reasons you mentioned.

I have an old G4 Mac with 2GB RAM and CS3 on it. I believe it is about 10 years old now. It could run 10.5 but I only upgraded it to 10.4. It sits in my attic as a backup. It is terribly slow, even with small web size graphics. It cannot even display YouTube videos smoothly. You can find similar models on eBay for $50. Cheap $200 netbooks probably have more oomph than that G4.

Do not think that you've inherited anything beyond the usefulness of nostalgia. I'm all for trying to get the most out of technology before it hits the landfill but you will waste much time and money trying to rehabilitate something so old.

If you are willing to consider the limitations of Elements, then you probably would have no issue with installing GIMP for free.

http://gimp.lisanet.de/Website/Download.html

The last G4 Power Mac was introduced 9 years ago in 2003.  That's as old as the Iraq war and older than Facebook. Better digital cameras of that day were ~5 megapixels. If you are limiting yourself to smaller images then you might be able to tolerate that Mac.

Buying old software is truly messy. This is complicated by activation. That license that you think has been purchased  legitimately as pre-owned software still has to be activated by Adobe.  By the time you discover that it cannot be activated, your transaction with the seller is complete and you cannot get a refund.

Mac is not essential for the professional graphic designer and photographer. One can use Windows computers at a much lower cost.

I think the platform bigots left some time ago.

PS 7 will not recognize a drive over 1T.  So if you have that large of a drive you need to install the data and scratch disk on a partition or a smaller disk.  Think the program can be installed on the larger drive.

If I remember correctly some have it installed on Win7, but not positive on that.  You can definately run it if your OS allows you to run in XP simulated mode.

I do have an older laptop with XP on it that I use for my scanning (Microtek apparently will not be releasing a 64-bit driver for my ScanMaker 9800), but it shuts down spotaneously at random times - sometimes it'll run for days, other times, it shuts down seconds after booting.

If I put Photoshop on it, I'd likely end up here asking, "Can I recover from a .TMP file after a crash?"