I don't think you'll need it. I've been using a Mac laptop for 18 months now and have never had a piece of spyware. My Windows desktop is continually infested. BTW, I went to Apple's website support section and searched on the word "spyware" and got no hits. It's just not an issue. You will never regret getting a Mac.
Thanks. We also have a pretty sensitive fire-wall installed in our wireless router; it keeps out a lot of stuff. I'll have to be sure to instruct the kids never to click on a banner ad!