I've actually answered this question (before even seeing it!) on your other thread.
I note that Gingejbee has recommended GIMP. It's an amazing program, which seeks to do everything that the 'full' versions of Photoshop do. Indeed, it's actually used instead of Photoshop by many graphic designers, magazine photo editors, etc. However (because there's so much to it) it's got a really massive learning curve and it's easy to be left totally bewildered by it (especially if you've never used Photoshop).
I'll stick with my recommendations of Irfanview (for basic stuff, such as image-cropping, removing red-eye and adjusting brightness and contrast) and Serif PhotoPlus SE (for more advanced stuff).
Links on other thread.