CDC compliant device

[Priya]

Hi,
I'm new to devic driver programming & USB technology.
I 'm writing a driver for a CDMA handset CDC compliant USB device.
It supports multiple interfaces.
I used UsbBulk.sys from NTDDK for performing read write operation. It fails.
I modified code for displaying multiple interface values. Do I need to change in any other file (eg .INF) for working with multiple interfaces.
I also need to write a Communication class for USB modem.
How do I write a vitual serial port driver ?
How can I proceed ?
Thnakx
Priya