It might be worth trying The Gimp or Paint.NET too. Picasa (by Google) is very good and I think that has brightness/contrast adjustment... even an 'I'm Feeling Lucky' button to auto adjust. All three are worth a try. You're only after a simple contrast/brightness adjustment really.
Thanks for the suggestion Syph. I'm downloading Picasa right now to try out. I'll let you know how it goes. As for the Photoshop program..., I'd love to get it but it is far too expensive