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No, there's been a lot about reading FDD over the years, as far as I know it's never been done sucessfully - basically you don't have enough memory in a PIC to do it.
You can certainly program one PIC with another, that's how the PicStart+ works - but it gets it's data from the PC serial port.
What you need is a microcontroller with code space for a bootloader. uC with this capability can write to their own flash memory while execuing code in a special section of the flash that can be read while writing the rest of flash. Most 8051s have this capability I don't know about PICs though. Bootloaders let you use almost any interface (RS232, ethernet, etc) to reprogram the main program. You can send users updated code through the internet and they can download it into your product with their computer.
Because you can't read just a byte off a FDD, I think you have to read a complete track, or at least a complete sector.
As 'bmcculla' mentioned, a botloader system could work fairly easily for you, various PIC's are bootloader capable - including the 16F876/7 series. All you need is a serial connection to a PC.
Interesting. Now you've got me thinking about how that could work.
The bigger PICs do have 1k of RAM space, capable of buffering the 512 byte chunk as long as you can do everything else you wanted with half the RAM already taken. I wonder, could you format it so that you only use say the first 128 bytes of each chunk and just forget about the rest? Or would the storage format need to use the entire chunk?
I saw some recommendations that an I2C EEPROM or a parallel EEPROM be used to hold the 512 byte chunk.
Here's some stuff I saw about interfacing with an MMC or CF card. I saw bootloading off the card mentioned.
A PIC alone won't be able to read from an FDD. You would need a floppy disk controller (FDC) to read a standard 512 byte sector. Stand alone FDC chips are getting harder to obtain. This alone will eliminate any cost advantage a FDD may have.
You may have to forego using DOS format for storage. There is not enough memory to decode a DOS directory, FAT, etc. even if you could read a 512 byte sector.
I2C is going to be faster than a floppy - remember the BASIC STAMP?, this reads it's interpreted BASIC code out of an EEPROM (byte by byte, as it's needed).
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