In most of our examples you will find a Dscr.a51 file included in the project. This file is where the VID/PID/DID as well as endpoint information, for the device that will be compiled into your .hex file.
If you use EZLoader (B0) and ReNumeration, you will program an initial VID/PID combination into the EEPROM which will call (via the .inf file) a loader driver which will download your firmware to the chip. When the 8051 comes out of reset your device will have the VID/PID of your downloaded firmware and will cause your device driver to be loaded.
If you link your code to internal memory and burn your firmware into the EEPROM for a B2 load, the chip will download your firmware over the i2c compatable interface and when the 8051 comes out of reset your device will have the VID/PID from your firmware and will load your device driver.