We present an incremental approach to developing programs for reconfigurable engines, systems which contain both instruction processors and reconfigurable hardware. The purpose is to support rapid production of prototypes, as well as their further systematic refinement and adaptation when required. The key elements of our approach include abstractions and tools based on high-level descriptions, and facilities for optimizations such as domain-specific data partitioning and run-time reconfiguration. The application of our approach is illustrated using the SONIC reconfigurable engine, which contains a multi-FPGA card in a PC system designed for video image processing.