I too am an Arduino newbie and would like to produce a similar Google Latitude GPS tracker and started looking into it a couple of months ago. I have not developed anything due to other commitments but will try and pass on what I found.
Jayesh has a good tutorial on Blogspot http://jayeshprojects.blogspot.com/2010/04/real-time-mobile-gps-tracker-with.html
for a Arduino GPS Tracker using Google Maps and a GPRS module, he uses Application and a SQL server as opposed to sending the information direct to Google Latitude.
From what I've read Google Latitude can only receive information in the form of java script, to overcome this Ben also posting on Blogspot http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1286813442
communicates from Arduino directly to the Google App engine then to wherever you wish.
a GSM Arduino tutorialhttp://tronixstuff.wordpress.com/2010/09/17/moving-forward-with-arduino-%E2%80%93-chapter-17-%E2%80%93-gps/
a GPS Arduino tutorial
Have fun coding,