I suggest you use a protocol as you mentioned. Kermit is probably not a good choice as it is all ascii characters, I would suggest Xmodem - it is supported by Hyperterminal and is simple to implement on the 8051. The maximum serial speed is as high as your micro can cope. 115200baud is not unreasonable. One problem you might come up against is the sector size of the flash device - on the AMD parts it can be 16K and larger. You will probably want to have enough ram to buffer the sector size. In my designs I used a device with a 128byte sector size that suits Xmodem better (xmodem uses 128 byte packets).