Hi pictures - I have the latest MBP running 10.5.1, Parallels Build 5582, XP Pro VM and Vista Ultimate under Boot Camp. I use Garmin Mapsource and BlueChart Pacific for my trip planning and I use the Garmin USB card reader to upload/download data to my GPSMAP 3010C chart plotter.
The USB card reader works OK under the XP VM using the latest version of Mapsource. However, I have not been able to get the Vista VM (created from my Boot Camp partition) to recognise the card reader.
The USB card reader works fine with Vista under Boot Camp.
Not sure if this helps your situation, but for me, at least I can use the convenience of Parallels XP VM for trip planning and upload/download with my USB card reader. I can also do my trip planning with the Vista VM, and if necessary, fall back to Vista/Boot Camp to use the USB card reader.