This map is a simple kml file overlaid onto GoogleMaps. A Jabber robot collects all of the Location data about users in it's roster (buddylist) from their vCards and then converts that data into real world co-ordinates and generates a kml file, which is then overlaid onto the map. This means that unlike most other Jabber map implementations on the 'net, you don't have to manually tell the bot where you are.
To add yourself to the map, just send a subscription request to the robot's jid: firstname.lastname@example.org and make sure you have the relevant information setup in your vCard entry. Geolocator uses the 'locality', 'region' and 'ctry' fields of your vCard to get your location. The plan is to eventually use the gelocation data that is defined in the XMPP Protocols XEP-0080 and XEP-0154 when more clients begin to implement them.
Gtalk users unfortunately cannot display themselves on this map, because Google have not implemented the vCard specification properly (sadly) leaving out the location information. If you're a Gtalk user, my advice is to get a proper standards-compliant Jabber account. If you add Geolocator to your roster you will appear, but obviously not in your real location, instead you'll find yourself huddled together with the other disgruntled masses outside the Google Campus in California chanting "We want real Jabber compatibility!!".