It's called Brownfield development. Manning publishes a very good .NET oriented book on it, but many of the concepts can be applied to any language or tool. I wrote a blog post about a Brownfield seminar I attended. It was presented by one of the book's authors. http://www.craigberntson.com/blog/?p=869

>A lot of advice could be described as greenfield. Where are the strategies and tools for the realworld.