I read in article recently which had a very wise comment by the author. He was talking about standards complaiance and whatnot, and mentioned that a big problem keeping people from being more compliant was NS4. Also, given that so few people (like 5%??) use NS4 now, that the way to force the remaining people to update is to just forget it.... design for the standards compliant browsers using CSS, XHTML etc, and those last remaining NS4 people can either deal with it, or upgrade.
I am SO in agreement with that sentiment. There is no reason to keep kludging code and hacking to make things work with NS4. It's an old, crappy, bug ridden browser, and we need to force people away from it. Anyone still stupid enough to like using it, well that's their problem then. If they don't like IE, there's plenty of other browsers to (Opera does a commendable job)