Requirements Engineering (RE) is a multi-faceted discipline involving various methods, techniques and tools. RE researchers and practitioners are emphasizing the importance of having an integrated RE process. The need for an integrated toolset to support the effective management of such an integrated RE process cannot be over-emphasized. Tools integration has been identified as an important next step toward the future of requirements management tools. This paper reports on some of the significant architectural and technical issues encountered and the lessons learned in the process of developing an integrated Requirements Management (RM) Toolset: PARsed Natural language Input Processor (PARSNIP) by integrating various independent tools. This paper provides insights on architectural and technological issues typical of these types of projects, the approaches and techniques used to address the architectural mismatches and the technological incompatibilities.