Steve Jobs has a reputation for taking a 'reality distortion field' with him wherever he goes, but, even at its highest setting, the RDF can't hold a candle to whatever it is that has been interposing itself between Bill Gates and reality lately.
Rather than rehash arguments that have already been made better than I could by others, allow me to point you to John Gruber's Daring Fireball weblog. (Just scan through the entries of the first few days of February.)
While takng Gates to task for grossly misrepresenting the relative state of Vista security versus that of Mac OS X, Gruber concedes that it might be true that Vista is more secure than version 10.4.8 of Mac OS X.
What Gruber migth have said and hasn't yet, that I've noticed, is that even if true that's likely to be a very short-lived state of affairs. The release of 10.4.9 might put Mac OS X back in front, and if not that then 10.5, due within the next few months.
But even without any improvements to Mac OS X security, that of Vista is sure to degrade rather rapidly, once it gets into the hands of the people who write the malware that has so dogged previous versions of Windows.
I invite you to recall that the kernel of Mac OS X is open source software, whereas the source code for Vista hasn't even been shared with the companies that write security software (unless that's recently changed), so the current state of Vista security is at least partly a matter of secrecy, secrecy that will succumb to the techniques of reverse engineering sooner or later.
Moreover, Gates' challenge to produce a "total exploit" of Vista once a month is all too likely to be taken up enthusiastically by an assortment of hackers and crackers with the skills to do that and then some.
Bill Gates had managed to build up a little credibility in recent years; now he has none.