Ciao Roberto , b 4 installing the 1.4.x update the system should verify the DVD , if the dvd it's verified then the problem must be in some procedure during installtion .
any way I suggest you to do not install the complete language package , use italian only it will use less HD space and I think it will speed up Spot Light indexing .
About Spot light : you may found the new OS get slower in the first days , that's normal. I suggest you to keep your G5 on all night , the next day it will be faster .
Ciao
why I did wrote this in english ?