Yep but then not all computers are windows
With the current limited userbase of MACs and the fact that most virii scripters target the largest and easiest userbase (currently windows) it is safe to assume that a MAC has probably a 99.9% chance of being virus free
Anyone who says differently is just scare mongering..
It's a shame really as MACs have this reputation purely based on limited numbers and if they do become "popular" then they will be targeted a lot more (hence my comment about the iphone/ipad in a previous post)