You'll need to go with a 3rd-party (aftermarket) solution for it. Other owners have installed actual in-car systems, and some have hooked GPS receivers to their laptop computers or PDAs and carry them in the car. Both have worked.
If you go for an in-car nav system, you'll need to put another screen somewhere.
I just installed a Navman iCN 630 in my MO. I t works very well and has voice prompts. I also like the fact that I can take it with me if I take another car. I mounted it at the top of the windshield, just to the left of the rear view mirror. It sits a little higher than the rear view, so it is mostly hidden by the tint strip and not very visible from the outside. If I am too lazy to remove it and hide it at night when I stop at a hotel, I can just lower the sun shade an it is almost impossible to see.
The only problem I have right now is I have a cord hanging down the middle of my windshield and dash! Navman does not yet offer a hardwire harness, so I will have to figure out where to get one or how to make one. The Navman requires +5 vdc, 2.5 amps and looks to have a standard PDA style tip. I can get an extra cig lighter adapter to do surgery on, unless someone knows where I can find a harness that would work. I want to tap into the lights above the rear view mirror. Engines I can work on, electrical is not my thing!
The clear plastic lens' on the lights pop out, from there it's not too tough to pull out the whole assembly. (It's been about 5 months since I did it but I don't seem to remember anything but it being clipped in.)
Once you get this out, you can find power to tap off, there for the lights. If you don't have one, go to Radio Shack or Home Depot and buy a cheap multimeter. RTFM and practice on some batteries. Then use this to check where there's constant power. You'll have a very useful tool and have taught yourself a new skill.
From there, you can figure out how you want to connect in. Modifying an existing cigaratte lighter adapter is probably the least painful. Remember to keep it fused. You can get an inline fuse and hide that in the headliner. RS also has lots of small power connectors you can select from to attach to. They also used to have crip on connectors that would allow you to tap into existing wires without cutting them. If not, you can take some wire strippers and just cut into the insulation, without cutting the wire, and pull back the insulation enough to wrap another wire around it. If you're good at soldering it, you can, but otherwise, just tape it with electrical tape and it should be fine, as long as it's good and tight.
I unstalled a Vcommand navigation system in my Murano. It is pretty cool. There is no screen, and the only parts that you can see after the installation is the microphone and power switch. Otherwise it is all voice commanded. I was a bit sceptical about the screenless operation, and it ability to recignise your commands, but I love it. I was used to the screen/joystick based system in my Mercedes ML, and this is so much easier to input your destination. It also uses a internal hard drive with the whole country on it, and has a portable kit so I can use it in a rental car or otherwise. One last thing. For the sleepy lonely trips there is a game, Blackjack, the dealer even has a New Yorker accent... It is pretty entertaining....