I joined a small development team that was rewriting their core systems from scratch because their legacy cobol-based systems were maxed out in terms of performance in addition to not being Year-2000 compliant. Our team was responsible for implementing everything that the thirteen old system did as well as new functionality in a year. The legacy system was extrmemely complicated, but we successfully converted all the core systems in 9 months while using the remaining 3 months for extremely thorough testing. The greatest challenge proved to be educating the user community about GUIs and the mindset and approach necessary when moving from a text based interface to a rich GUI.