There was a strategy guide for the Japanese version of DD, but none for the English version. The Taiwanese version was distributed with a cloth map. CDV had a coupon or ad in the German version for a DD key chain and coffee mug, IIRC. None of the other publishers did much in the way of extras, AFAIK.
A couple people have done walkthroughs for DD;
LISTING OF INFO, TUTORIALS, SPOILERS...
