As for accessing SQL data directly, there is an article posted on the Apple Developer Connection. Accessing the database in ARD 3 is a little bit different than in earlier versions because it needs to be compatible with an existing default postgreSQL install and more secure than ARD 2. The database communication is also on a different port (the new port is 5433 by default) and the username and password can be found in this directory: /private/var/db/RemoteManagement/RMDB/passwd.txt.

The default username is ard but the password is generated randomly so each install is unique and secure. With ARD 2, we set the username and password to ard/ard. As with ARD 2, however, the user can shut down the agent, edit that passwd.txt file to change the username and password and then restart the agent.

One of the greatest selling points in ARD is the fact that there is no per-client licensing. Since ARD client is built into every Mac OS X 10.3 and 10.4 desktop and server, the only expense in ARD is the administrator license. This license is sold in two tiers: For $299, administrators can manage up to 10 machines at once -- or they can manage more than 10 machines, but only 10 at any one time. For $499, administrators get an unlimited usage license.

Unless you have just 10 machines, I advise buying the full license.