Back in the day, I was one of a handful of people trying really hard to get things to look nice on browsers like Netscape 4, Mac IE5 and IE4 - at the same time.
Innovation in this area has moved in leaps and bounds in the intervening years, so this information is kept here for archival pursposes only.
This is a simple method of targetting rules specifically at just macIE5.
It relies on the curious fact that macIE5 apparently gags on a backslash in a /* comment */ and forgets to parse the following rule.
Since putting this test page together I've since found that:
The comment must be inbetween rules, not within a declaration block {}.
If the following rule's selector is an element (e.g body), the hack fails, it needs to be a . or #.
(I suspect the significance of this is that class and id selectors start with non-alphanumeric characters, and for some reason the parser fails to ignore the commented backslash and tries to escape the next uncommented character it finds -- resulting in an invalid rule)
Whatever the cause, this opens the door to working around that irritating affection macIE5 has with horizontal scrollbars...
This goes some way towards a viable workaround. A couple of issues remain open, but there are no horizontal scrollbars, and other browsers are unnaffected - by my testing at least.