1. if you want to buy a new TT - don't buy anything running on NC10
2. if you already bought a device running NC10 and you still have the chance : take it back and get a refund. A refurbished Go520/530/720/730 is still the best way to go.
3. if it is already too late for, or you are just interested : keep reading ;

Currently there is no way to access a device running on NC10 other than using the MyTomtom app on your PC.
You wont see it in the Windows Explorer and the device won't show up as a drive letter, therefor you can not access it.
Why? TT uses a new file system whis is a modified Linux system. It uses a filesystem that Windows can not handle.
If you want to use a new/different map than you have to buy it from TT in case you have no free maps included in the purchase.
Same goes for modifications or additional software like ttmaps or tomplayer - only if they offer a installer for MyTomtom you can install them but still you are not able to add any further content at this stage.
Adding own POI's should now be possible using MYTT.

You don't have to ask on how to install a new map for your device or how to get premium voices working : not possible right now!
You don't have to try to install a new NC to "upgrade" your device : no access means no copying of a new NC onto the device and no patching possible.

As long as noone provides a DLL/plugin/program to access the file system you can only use MyTomtom to play with your device.