If you choose to download config from server, agent sends request for configuration file to server when it starts. Each config stored on server has filtering script associated with it. Server runs those filtering scripts one by one until one of them returns true, then associated config is sent back to agent. Filtering script receives the following information for evaluation:

$1 - agent's IP address
$2 - platform name (like "windows-i386")
$3 - agent's major version number
$4 - agent's minor version number
$5 - agent's release number

For example, filtering script for all Windows agents with version >= 1.1.0 will looks like following:

return ($2 like "windows-*") && ($3 >= 1) && ($4 >= 1);

Best regards,
Victor