SVG (Scalable Vector Graphics) is a modern technology, allowing to show vector images on web pages. A family tree in SVG format can be scaled in the widest range! To see the tree in this format, your browser should support SVG. If your browser is Mozilla Firefox or Opera they already have built-in SVG support. Internet Explorer requires special plug-in, for example, Adobe SVG Viewer which can be loaded free of charge from here (version 3.03) or here (version 6.0 alpha).
Since Adobe SVG Viewer works faster it is recommended to install it in yours Firefox or Opera, replacing their built-in SVG engines.
Installing Adobe SVG Viewer in Opera is similar.
About SVG support and Adobe SVG Viewer installation in different browsers see here.
About SVG support in "Relatives" program see here.