Google Earth and GooPS are a good combination. With Google Earth v5 you don't really need GooPS because GEv5 has support for a GPS receiver built in. But it's a real bear to get working. GooPS does only one thing. It helps you connect your GPS receiver to Google Earth. And it does it really really well. Since it's free, I consider it an absolutely necessity if you want to connect a GPS receiver to Google Earth and don't want to risk having to tear your hair out.
Google Earth does not provide voice guidance. If you are planning to use your UMPC for vehicle navigation, you really should be considering voice guidance. It is not safe to be trying to use your navigation device for visual guidance while driving.
Google Earth does not contain maps. You need an internet connection, preferably high speed, for Google Earth to access the maps. Google Earth v5 has a built in cache for map data. It holds about 2GB of map data for use offline. So it is theoretically possible to use Google Earth v5 (preferably with GooPS) for realtime navigation. As long as you can get the right 2GB of map data into the cache.
This is a really tedious process, especially if you want the detailed maps loaded, because you have to actually browse those maps at the detailed level for your entire trip to get it all into the cache. And there's no way to know when you reach a point that you've overflowed the cache and the new parts you are browsing are pushing the old parts out the back.
There are supposed to be utility programs out there that help you load the cache more easily, but I have not been able to find one.
Google Earth was never designed for realtime navigation so I don't mean to criticize it. Just letting you know the limitations.
If you want to try out a program that is a little better for that purpose, you can download a free trial of Microsoft Streets&Trips. If you go to the Streets&Trips section on here and look in the top thread that reviews Streets&Trips, there is a link in there to Microsoft's free trial download for it. Or you can just use your favorite search engine to look for "Streets & Trips trial download" or something similar. It's fully functional, no silly tricks. It just stops working at the end of the trial period if you haven't bought it yet.
...ken...