Hi,
You do not need to write one, it is usually sufficient to use usbser.sys.
If you are building a modem, then
http://support.microsoft.com/kb/837637/en-us
may be what you are looking for; if it is not a modem, then the approach=20
described as "not recommended" in the KB article (that is, directly=20
referencing usbser.sys from your .inf file) may be the best option.
Simon