I was looking for WinUSB examples all over the Internet last time but to no avail.
The only one I got is an incomplete example from Microsoft.
Luckily some Microchip Forum posters have come out examples for Visual C++.Net and Visual C#.
Mike Zoran's USB Soundcard and RFModem examples include Visual C++.Net based host software to update the firmware inside PIC18F2550.
J1M has examples for Visual C#.