I'd have to disagree about PNG if this is something that will reside on a website. It's an odd thing but I had a problem where any NT 4.x computer running IE 4.* would totally freeze solid and requirie a hard reset when trying to view a client site. It turned out is was becasue of a PNG on the site. Granted they are both old software but if appeasing consumers is the goal, giving them a hard boot is not the way to do it.