This paper proposes a novel methodology tailored to design embedded systems, taking into account the emerging market needs, such as hw/sw partitioning, object-oriented specifications, overall design costs and early analysis of design alternatives. The proposal tackles the problem by considering UML as the starting point for system-level description and uses a customization of Function Point analysis and COCOMO to provide cost metrics both for hardware and software. Finally, a genetic algorithm is used to select the best candidate architecture. The paper also reports some results, obtained from a case studies, showing the viability of the proposed approach.