Lpc2000

I want to make my USB Headset using LPC 2138 .This is my first time to 
use USB.
How do I tell PC that it It has to send or recieve  encoded audio 
signal to the USB.
Do I need to write saperate device driver for windows or Human 
Interface  Driver(HID) will takecare of it..


Plz help ..

Thanks and regards

Girish