use the healing tool (looks like a bandaid). ALT+click on an area that looks similar to the area you want to fix. Release, then go to the damaged area and click and paint over the mark. Voila! you can also use the clone stamp or patch tool in a similar way, you may wish to save the original and experiment. The clone stamp will just paint in whatever you ALT-clicked on (the source) and I can't remember exactly what patch does. Healing will somewhat preserve the original texture and tone of the area around the damage.
you can pm me if you need more photoshop help, all that time at design school gotta be good for something!