Thanks a lot for your response.
I have used two laptops, Snow Leopard + Virtual Box, and although one was more faster (because of a faster processor), still is too slow and I had to stop the process. The setups are the following:
Machine 1: VB RAM = 1GB, VB HD = 25GB,
Machine 2: VB RAM = 2GB, VB HD = 25GB
Unfortunately I did not have enough time to track/debug the problem and therefore I am using and old version of my customized dvd based on knoppix 6.4 .
Actually, the customization is really simple, just adding some packages to the dvd.
Anyway, I wil try to test in a desktop later to see if the problem replicates.