I always sub soy milk for milk in any receipe. it has always worked out so far. for butter you can sub margarine, or in baking i have used canola oil and/or applesauce as a sub for butter. they also make soy margarine.
i have IBS and follow a non dairy diet as much as possible. there is a message board on this site with receipes that might be worth checking out for those of you that can't eat dairy. there seem to be lots of vegetarians on that board as well so plenty of veggie friendly receipes.http://www.helpforibs.com/messageboards/ubbthreads/recipe_index.php