These instructions where tested on Ubuntu 9.04, but should on any distro. I am unable as of yet to get the newest version of MapSource working, so I used an older version.
You must first have the MapSource CDs. Mine were version 3.02
1.
Download Mapsource 6.15.62. Install MapSource from your CD. Create a new bottle, based on Win2000. Call it MapSource. It must be a win2000 bottle
3. After installation is complete, immediately install the downloaded update into the same bottle you just used.
a. The install will appear to go very fast, almost too fast. This seems to be normal.
4. Execute the following at the command line:
sudo modprobe garmin_gps
5. Then, execute this command:
sudo ln -s /dev/ttyUSB0 ~/.cxoffice/MapSource/dosdevices/com1
6. You should then be able to start the MapSource and interact with your GPS.