the option 'enable infrared' is not in the security perferences, the option 'enable infrared' is not in the security perferences

The setting is in System Preferences/Security/General - uncheck the box Disable Remote Control Infrared Receiver.

If your remote does not not work, check its battery, and also try 'pairing' it again:

How to Pair your Remote to your Mac:

http://support.apple.com/kb/HT1619?viewlocale=en_US

in the security window is an advanced button, click on the button and you will se the option there.