Vehicle Tracking Server
The vehicle tracking server is a computer running software which can retrieve (and display / report on) position data sent from the from the GPS tracking device installed in the vehicle.
For a simple ready made solution, GPS Gate offer a free BuddyTracker service, and a commercial Vehicle Tracking application which can either be obtained via a subscription service or as an application installed on your own server. Generally these services are accessed via web browser however software for PDAs / mobile phones (to allow for tracking on the move, and away from a computer) is also available. Note when choosing server software ensure the unit software is comparable.
The server does not necessarily need to be anything special, nor does it need to be running any particularly resource intensive / expensive software. In its simplest form it may be a small PHP script running on a standard web server (PHP is compatible with most hosting platforms) which logs the data, and displays it on a Map. For a publicly accessible website a solution based on the Google Maps API along with Microsoft Virtual Earth SDK can be used.
On the more advanced / commercial end of the scale some may prefer to implement their own backend server applications bespoke to their requirements e.g. delivery courier tracking / taxi job dispatch management using technologies such as PHP, and MySQL which now has Geospatial support. Along with a commercial mapping provider such as Multimap.