Vicky and I made a trip there last year. It was awesome. It's true what Dave said about detectors. If they find one in your car, even if it's dismantled, you'll lose your detector, your car (so I was told) and get arrested and fined.
I was fortunate enough to stay at a B&B that was on the battlefield but out of the national park. I asked the owner if I could do a little hunting and she said it was fine (boy was I excited!). Then she told me that the previous owner was a MD'r and his club hunted the place every week

I found some reproduction buttons and then I found this:
<img src=http://render2.snapfish.com/render2/is=Yup6aQQ%7C%3Dup6%3DzqH%3AxxqUD7qRUrKxzX7BHpUUKxgXPJP%3F87KR6xqpxQQ0nxaJexelexv8uOc5xQQQ0QGleJQolPqpfVtB%3F*KUp7BHSHqqy7XH6gXPJP%7CRup6eaa%7C/of=50,449,443>
I would highly suggest that you hire one of the tour guides to go with you in the car. A little pricey, but well worth it! Also drive down to Antietam and Harper's Ferry. If you want the audio tour for Antietam, I think we still have it. It's a CD tour with a map. Before you go, watch "Gettysburg" and "Gods and Generals" GREAT movies.
I walked onto the field where Pickett's charge took place. It's like the ground talks to you. I walked on little round top and big round top, even walked through Devil's den. Wow. It's hard to comprehend.