Hi there,
From memory, page-break-before and page-break-after are CSS2 properties - hence only CSS2-compliant browsers support them. I don't think NS4.x supports CSS2 (and only partially CSS1) - unfortunately I can't think of a clean solution to your problem (unclean: use tables with absolute heights etc, but then you have to work out what sort of paper the viewer is using: A3, A4, Foolscap and its orientation: portrait or landscape)