There is an interesting article in the Apple Developer Connection site which comments on some CSS issues and solutions with Internet Explorer (IE) version 5 on the Mac for OS X and OS 9.
Although being more compliant to standards that IE for windows the Mac version has some problems when rendering CSS DIV tags with absolute positioning. There is also some minor problems with overflow declaration and margins. The article comments on some alternative solutions
http://developer.apple.com/internet/css/ie5cssbugs.html
Here is another page which comments on a similar IE 5 DIV Float issue. The site contains a nice collection of highlighted issues, bugs and oddities
www.l-c-n.com/IE5tests