I agree that a textile conservator may be able to give the dress the best care, however, depending on the condition of the dress, the first step for some textile conservation projects is to send them to a specialty dry cleaner. So, the dry cleaning may be all you need done. If you go the conservation route, I'd recommend asking a lot of questions at the consultation to help you determine what level of cleaning you really want (and want to pay for). I don't personally have any dry cleaners to recommend, but Museum Textile Services (http://www.museumtextiles.com/conservation.html) in Andover does good work if you do want to take it to a conservator, and they do take private clients as well as museums.