That chestnut's been around for a while. While fairly accurate, it refers to a PC running Windows XP RTM from 2001 (so without even SP1 applied) and the infection spoken of is usually a drone exploiting the unsecured Messenger Service to display advertising, which while annoying, isn't particularly sinister.The Register today reports that an unpatched Windows PC connected to the internet with no firewall or virus protection "is likely to be infected within 4 minutes".
Disks of that type haven't been sold for 5/6 years now, so it hardly paints an accurate picture of the fate beholding an unpatched Windows PC running Vista or XP installed from a newer disk with a service pack added (even an SP1 disk is inherently more secure out of the box than RTM).