A lot of malware and the like works by running scripts that install shit or w/e when you visit a website, so if you don't let the scripts run (which is what noscript does) then you eliminate most of the problem. (The other problem is downloading programmes that are virus-laden, but well...that depends on the net-savviness of the person.)

I wouldn't say that Macs are necessarily safer than Windows...(although I'm tempted to say that about Linux, if only because whotf wants to hack Linux computers anyway), either. It's really a matter of personal preference in deciding what OS to get, in regard to interface and the like.