The code is here.
You will need to get the flashable USB PIC, the PIC18F2455, PIC18F2550, PIC18F4455 or the PIC18F4550.
This code example emulate a com port over USB.
The bootloader, you can also get them from microchip with the bootloader windows application example, done in VB as far as I can remember.
You will need to adapt the asm code for the pic you chosen. Not hard to do, just plenty of reading and understanding the datasheet.
Learn to use asm, they are much more flexible for critical application. Beside alot of the example are in asm you will miss out alot.