The success and importance of a production infrastructure is measured by the interest and engagement of user communities when utilizing it for their own benefit. It is crucial for a new infrastructure and technology to attract users. However, the utilization of complex infrastructures such as Desktop Grids is far from being trivial. Porting applications to this platform requires specific tools and approaches that end users may find challenging to engage. Therefore, it is crucial to provide support for potential targeted user communities, and to port and aid the deployment and running of their applications on the target platform. This chapter gives an overview of the challenges and available tools and solutions when porting applications to Desktop Grid infrastructures, especially when these infrastructures are extended with additional resources from service grid environments. The chapter introduces the EDGeS Applications Development Methodology (EADM) that provides a generic framework for porting applications to Desktop Grids and combined Desktop and service grid platforms. It also analyzes the requirements toward applications to be run on combined desktop and service grid platforms, and describes the most common user scenarios in these infrastructures. Finally, it illustrates the utilization of the methodology, the proposed tools and user scenarios via experiences gained through real-life case studies.