If you have a basic 2M packet station you can get started in APRS. APRS is based on packet. To start at home, download one of the APRS programs depending on your preference, DOS, Windows or Mac. Set your 2M radio to 144.390 Mhz simplex, connect it to the TNC, connect the TNC to the computer, run the APRS software and configure it so that it can talk to the TNC and you should be all set. The APRS software will want to know your position. Mobile stations usually interface a GPS receiver with the TNC. If you are at a fixed location you can just key in your coordinates. If you don't know your coordinates use MapQuest or any other mapping program to find the coordinates of you fixed location.
With APRS running you will see a map of you area and you will see icons representing the other stations on the air in your area. Mobile stations will move. You communicate with others by sending single line text messages. Just like packet you can set-up a beacon text.
APRS uses the existing packet protocol concept to communicate. The software creates a network what digipeats the info around the network automatically. The position information of the various stations in passed along in the packet messages. The position info is just stripped out by the computer so you don't have to see it each time.
APRS is geared toward public service type support. The idea is to graphically show resources or conditons and also permit stations to send simple text messages back and forth. By the way, icons show up on the map either because they are APRS stations, or because someone has manually placed the icon on the map.
APRS is pretty neat and it give you something new to do with your old packet equipment. The software, like most amateur radio software, takes a little time to become proficient with.
I started with an old PK-88 TNC, a 286 computer and an HT. This works fine from home with the DOS APRS software. I can't use the PK-88 in the car with a GPS receiver because the PK-88 can't understand the data from the GPS receiver. I also have a PK-232 and I was able to upgrade the firmware so that it can recieve data directly from the GPS reciever. Most TNCs build since APRS came out can communicate with GPS receivers. Some of the new Kenwood radios can operate APRS with just a GPS receiver attached, no external TNC.
If you get APRS running you can see youself on the internet at http://maps.aprs.net/MYCALL
were MYCALL is the callsign you are using, i.e. KA9ZIM-9.
Dan - KA9ZIM