  "Netscape Communications on Thursday launched the latest version of its Web browser amid mounting evidence that most Internet surfers are choosing Microsoft's Internet Explorer instead. " Netscape's browser share is 3.4 percent!! That's less than Apple's computer OS share, and I know of plenty of projects that have blown off Mac support. There's your argument not to worry about Netscape 4.x, and all the headaches that comes along with it, not to mention the time and money it will cost your client. 
