If you're having issues with the Deployment Agent on a VMware ESX 3.0 server not being able to communicate with the Deployment Server, here's a fix.
In addtion to the lack of communication, look for log errors that look like the following:
Debug: Error:Connection refused, connecting socket 3 to host at <DS IPAddress> 402 ... Warning: Error unable to connect to server
The problem is that you need to open port 402 so your server can communicate with the DS.
From a command prompt on the ESX server run the following commands.
esxcfg-firewall --openport 402,tcp,in,adlagent esxcfg-firewall --openport 402,tcp,out,adlagent esxcfg-firewall --openport 402,udp,out,adlagent esxcfg-firewall --openport 402,udp,in,adlagent
Afterwards restart the adlagent (./adlagent restart) (found in the /etc/rc.d/init.d directory)