System wide fonts are quite tricky, as we're transitioning between two font systems. Red Hat uses some custom hacks to Qt for instance to make it use fontconfig.
In general I'd wait until Mandrake provide an update. If you must tweak, then you want to install and setup fontconfig, update Qt, use GTK2.2, ensure XRender is up to date, use the latest FreeType and compile mozilla with xft2.
You don't actually need to update your X server however.