Those are some good shots!
Oddly enough Sounds Good and I were just discussing different photo editing software... There is a free program called GIMP that you could use to edit those pics. There are other paid programs you can use as well depending on if you are using a PC or a MAC. Programs such as Paint Shop Pro or Photoshop Elements for PC and iPhoto, Pixelmator or Apertature for MAC. Whichever one you choose, you'll have to tinker with the different aspects such as Brightness, Contrast, Saturation and other settings... keep in mind though that there is no guarantee you will be able to improve them and if you are able to do so, the changes maybe extremely subtle. Jim's right... it's not an easy thing to do and for a lot of photos it cant be done at all.