In case someone else needs to know this....I used the Garmin webupdater software to update my 305 firmware from version 2.8 to 3.2. The process is not without glitches.
The webupdater downloads to my computer (Mac) and runs fine. However, the Garmin must be turned on before the updater will run flash the firmware. Even then, I had to run it 3 times before it worked.
But, here is the tricky bit. After running the firmware update, the updater offers a second update referring the the GPS chip set. I ran it, multiple times, and reduced my Garmin to a paperweight that would not lock onto satellites at all. Finally, just guessing, I turned the Garmin OFF and ran the GPS chipset updater again. That did it, it works fine.
So, GPS ON for the firmware update, then turn it OFF for the chipset update. At least, that was my experience....