According to reports on Apple's Support Discussions forums, an upgraded graphics card could cause kernel panics when attempting to reinstall Mac OS X Leopard from the original, included restore disk.
-system -<BR>Powermac 5500/225<BR>OS 8.0<BR><BR>This will boot without extensions. Without bypassng them, the OS starts to load from either the CD or from the HDD but stops before any extensions ...