This is a correction. Somehow i managed to delete the IrfanView paragraph before posting the first time.
When I bought my PC with XP already installed I discovered a product called MS Photo Premium 10. This is 'embedded' in the "MS Picture It! 10" producct in the Start, Programs list.
This gets you to Microsoft Picture It! Library which is (to me) an unnecessarily complex product. But the Photo Premium 10 program is pi.exe in the "C:\Program Files\Picture It! Premium 10\" folder.
You may also have MS Photo Premium 10 as an option in the Open With list you get when you right click a .jpg file.
Various image processing and enhancement options are in the Touch Up menu.
IMHO the Colour Auto Fix imparts a brownish tinge to images compared with Photoshop's Auto Colour Correction, but that apart the MS program is pretty good without the need to get something else.
For a free download I would strongly recommend the brilliant IrfanView program from
http://www.irfanview.net/ This is my own default image viewer and contains a number of enhancement capabilities.
I frequently use its batch processing facility for things like resizing or adding borders to sets of images.
But i use Photoshop Elements (not free) for serious enhancement.
A product called The Gimp gets good reports although I haven't used it myself. See
http://www.gimp.org/