In Using vLite to put Vista SP1 on a Diet! I explained how I used vLite to almost halve my Vista SP1 install from about 10GB to about 5GB. I also linked there to my tutorial Creating a vLite SP1 Install in 32,767 Easy Steps.
Finally, the excellent SimpleHelp website has a tutorial How to create a custom Windows Vista Installation DVD. When using vLite, the more tutorials, the better. While vLite performs a great service for those of us who need to slim down Vista, you need to plan before you click.