The bootloader uses WinUsb.
1. Search the web to find a doc called "How to Use WinUSB to Communicate with a USB Device".
2. Download the DDK from Microsoft. I'm using 7600.16385.1.
3. Download the source files for the JM60 Bootloader firmware.
4. Add the various defines form the bootloader to your GUI code for things like mVERIFY, mPROGRAM, etc.
5. Download the free version of BusHound. Monitor the Freescale GUI USB exchanges for a bit, and you'll get the idea.
You'll only need a half dozen or so files from the DDK to use WinUSB. The bootloader uses control transfers.