Considering Garmin has a rough time with USB on "real" PCs, don't be surprised when it doesn't work with Parallels. In our GIS classroom in which GPS receivers are used, we had to stop using Garmin USB connectivity to the individual lab computers. 3/4ths of the Garmins would sync. The remaining computers would not. Too unpredictable and a management hassle in a classroom enivronment. The issue was frustrating enough that we decided to not use USB.
Alternative was to use the far slower, but nearly perfect serial access.
Likewise, the same situation exists for me with Parallels Desktop. I use a Radio Shack USB to Serial adapter and I have perfect communications. Click on the link below to read a message I posted that included how I use my personal Garmin 76CS with my MacBook. I was all but quaking with excitement as I was typing that message:
http://forum.parallels.com/post11862-11.html
Last edited: Jun 19, 2006