How can I start the ARD client on my headless server?

The easiest way is to have ARD started with the Server Assistant we you do your remote install. Failing that you can use the kickstart command:

See Apple KB#107837 for ARD 1.2.1-1.2.4

or

See Apple KB#108030 for ARD 2.x

ARD 1.2 and earlier don't use kickstart, but you can still start it remotely. See Apple KB#106981 for more info.

FAQ Manager » OS X Server » How can I start the ARD client on my headless server?