This is why I dont upgrade from Tiger to Leopard (or to any major system update)

The problem is , they will be lots of incomparability . Leopard has new security features and it causes a havoc when you upgrade from Tiger. This is why I partitioned my Hard disk into 2 partitions , one for Tiger and one for Leopard. Once Leopard is ready , I'll just delete the Tiger partition and use it as a storage drive