To program the C166 mcu, 'memtool' software can be used to do the job... How to program the C51 mcu???
"I would think we would have to know the specific processor he is using to answer the question." Yes. For variants with on-chip Flash, such software is usually available from the manufacturer's website for the specific chip. For variants without on-chip Flash, the target hardware would have to be designed to support software download, and the PC software to send the download would have to be designed to match the hardware.
All of the FLASH programming utilities that I'm aware of are listed at: http://www.keil.com/flash/utilities.htm If there are others, please let me know. Jon