As a consultant who occasionally switch hits as a tech writer, I'd like to point out that you will also have to do something about the lack of documentation for this system. In fact in the best of all worlds, this would be done before doing anything else. Had it been done already, you probably wouldn't have had this problem in the first place. At any rate you're going to need this sooner rather than later. Why not add it to the want list? Since a certain amount of the needed knowledge will have to be dredged up from the mess you've got, why waste that effort? Usually when I've been brought in to put out software fires, this winds up being part of the triage effort-- Just thought I should mention it, good luck!