We also have the DeLorme Street Atlas with USB GPS receiver. Put the little receiver box on the dash, plug it into a USB port on the laptop and start the software - it will let you advance route, select from POIs, or set in your location by address, etc. and you will have GPS on your laptop. All maps are installed from the disk to your laptop so there is no need for a data connection. It also has voice activation features - turn on the mic on your laptop and it will respond to questions like where am I, where it the next turn, how long to reach the destination, etc. This gives you the ability to not need to look at the map on the screen at all while you drive - MS Streets and Trips does not have this feature.
Using a laptop as a GPS really requires a passenger unless you have the voice feature that Delorme has. Traveling alone you have to secure the laptop where you can see it and have it not interfere with your driving - and have it out of your line of driving vision. It works great when a passenger can hold or be in charge of the laptop and pay attention to the route. A standalone GPS that fits on the dash or in the window is much safer when traveling alone.