A program that works good and costs nothing.

That's an oxymoron. You will have to spend some money to get good photo processing software - especially Photoshop.

The least expensive way to buy Photoshop is the way my friend used. He went on eBay and purchased Photoshop upgrade. This particular upgrade come with earlier version of Photoshop, like Photoshop II or III. You first upload the early version Photoshop and than upgrade it with the latest version. But even here, you will have to spend some money. My friend paid little over $300.00 for it.

Mac Book comes with its own image processing program in iPhoto that has good reviews. Of course, not a Photoshop but good for everyday's photo processing. Even though I own Photoshop I use iPhoto quite often myself.