Upgrade to Nav in '09 SL

[tecumseh]

My first post, purchased a '09 Murano SL this past weekend, with only 10.5k miles. Upgrading from my '00 Explorer with 178k miles, still running, expect the Murano to surpass that.
It has all the packages, except Nav. I do own a tomtom gps, however I would like to use the existing screen for my GPS. I have done a few searches here and haven't read anything but a youtube video of some guy upgrading to a touch screen. My questions are, how easy is it to do it yourself, and where do I need to start looking to purchase one?

Thanks