Are you sure you really want/need an antivirus system?
There are approximately 120 viruses for the Mac, not one of which runs in OS X (they are all from OS 9 and earlier). None of them are particularly harmful, to begin with. (there are thousands of viruses for Windows discovered every year, ranging from benign to horribly destructive, and they spread using back-access in programs such as Outlook, which is not on the Mac at all. All the tools viruses use to propogate and to destroy critical files do not exist on the Mac, and the Mac OS won't allow the kind of activity that most viruses would have.)
Word macros are buggy and all, but it's highly unlikely you've got any viruses at all. It's a much more secure system, and a much lower chance of viruses, than Windows...so much so that I have never even seen a Mac virus on any computer I've owned or troubleshooted, Classic or OS X.
While anti-virus software is one of the top-selling categories of software on the PC, anyone who tells you you really need it on the Mac is just trying to sell you something. I wouldn't worry about it! 🙂