Thanks jdstrung for this solution. It work for my 2505 and MacBook Pro running Mac OS X 10.6.6.When I first got my 2505, I could not get MyTomTom to connect to register my device or download updates. By accident I stumbled across the solution.
For some reason, when you first connect your TomTom to your Mac, the Mac thinks it is a network card and adds it as a network interface in the Networks Preferences Panel.
Pull down the Apple Menu to System Preference.
Click on the Network preference spanel.
If you see the TomTom showing up in the left hand pane, highlight it and hit the minus (-) symbol at the bottom left to delete it. Save and close.
MyTomTom should now connect to the internet and allow you to register and download updates.
I have seen reports elsewhere that the same problem may exist with some versions of Vista.
This needs to be made into a "Sticky" for all Mac users.