I went to visit Chateu-Margaux this autumn with my wife and her parents. It seems they are not very used to receive visitors, but if you make an appointment there is a woman that guides you through the winery.
It was a great experience, particularly the wine tasting that is included in the visit. However it is not like a fancy winery to visit, it's more like an old classy Chateu, a piece of history. Recommended only for wine lovers.