I totally agree with being honest about the charge. If you don't and they do a background check, even if it comes up that the charge was dropped, you are then looked at as a liar or at the very least, untruthful and that would probably ruin your chances of getting this position more so than being truthful.

Explaining that this was a volatile situation with your h 20 years ago and that you have grown and matured and learned from the experience and have never had another issue like that since will go much further than to lie and not mention it.

Wishing you well and good luck!