Well, I have an old... err... "archival backup" of Photoshop 5.0 for Windows I can give you. Goodness knows if it's still relevant anymore.

There are always alternative programs you can use, like Paint.NET, GIMP, MyPaint...all of them being freebies.
Of course, each of them have their own pros and cons, so it's up to you to experiment and see which one works best for any given situation.

As for you re-learning/building up skill...well, the best advice I could give is to re-visit your older works, and see what comes up from 'em.
It's usually a good idea, since at least that way you get to see how far you've grown and how you can improve from there.

Hope that helps.

If you have a tablet then Artrage will be a nice choice. The functions of the free version are limited but it's possibly good enough for you.
The advantage over gimp and photoshop is its very easy to use interface (It replaced my pen an pencil 2 months ago).
Export to PSD format is also possibe, so it's compatibe to photoshop with all layers.

You could maybe try GIMP. I like it, but it's fairly similar to photoshop in function, but different in how you do things.

I only have copies of questionable legality.