Gary, the advantage of Macs is really just that there are far less of them.  Believe me, if there were as many Macs as there are PCs there'd be plenty of viruses for them and it suddenly wouldn't look nearly as secure.  Also, if Macs presented as rich pickings as PCs there'd also be freeware virus kits for Macs. 

Less Macs doesn't just mean fewer potential targets, it also makes spreading a virus much more difficult and slow.  The success of the iPod doesn't really have any bearing.  It's an Apple product that's used more with PCs than Macs.

Michael.