An old simple Adobe Photoshop CS2 (exactly the same as PS7)
can be downloaded here for free:
Adobe Photoshop CS2 Download - TechSpot
Serials are there.
I use CS2 and CS6 + Lightroom.
CS2 is much smaller, starts very quick and has basic options.
It is very good for changing quickly the size: For example 1200 x 600 for uploading photos!
I remember to well when I purchased it as PS7 many many years ago (something like 2003) and paid over $ 1000 for it!
There is a little nuissance, easy to be solved: A pop-up window which asks each time to register. One clicks on "no registration" but it pops up again.
This is because one has to do it as "administrator" on windows! Then the click "no registration", thats it!
The useful book Adobe Photoshop CS2 for Dummies is to be found very cheap on Amazon or ebay.