I'm so new to this area myself too that it requires others with greater knowledge to comment.
My understanding so far is that apart from a firewall for obvious reasons the other security apps available for Linux only serve to prevent the spread of Windows malware to other Windows users although these in themselves cannot harm a Linux system. I do believe though that it's possible to get a rootkit infection with Linux but I'm not sure exactly how or to what extent this may harm the system.
I prefer Firestarter for my firewall solution and also have RootkitHunter installed, that's it.
If any of the above turns out to be rubbish then no doubt we'll soon hear about it and become suitably informed
