Hello,
You didn't state this, but I will assume this is for virtual machine guest OS agent installs. If that is the case, Virtual Infrastructure Navigator (VIN) will actually automate the install of the Hyperic agent for you. VIN is included with vCloud Suite Enterprise and is an appliance install.
Otherwise, you can perform an unattended install of the agent by editing the agent.properties file in the agent install directory and then running the hq-agent.bat with the install switch.