Netscape is much more stringent about properly formatted HTML documents. If, for example, you use a <table> and there is no closing </table>, the table will not be displayed. If Netscape is in your target audience, make sure that all HTML tags (at least those that require it) have closing tags. Mind you, it's not a bad habit to follow even when Netscape ISN'T in your target audience.
To prevent this kind of problem from cropping up after a site has been deployed, make sure to introduce Netscape, Opera, Safari, and other browsers into your testing routine early in the development process. You might also benefit from occasional validator checks:
W3C Validator HTMLHelp Validator