Psyshack, if you get S&T please let us know what you think.
Here you can find a tour of the different features of the program:
http://www.microsoft.com/streets/
I had it for about a week but I haven't used it that much while driving. The advantage of using a Laptop for navigation is that you can take it anywhere and plan your trips ahead of time at home.
The program can also be loaded on a PDA or some cell phones but you'll need to get GPS hardware. The GPS hardware that comes with the program is intended for laptops and connects to a USB port.
For long trips I normally get a Triptik from CAA (Canadian AAA) but this program seems like a better option.