To install the 32-bit drivers from the cd, open "README_Ubuntu.htm" and "Scanner Installation Guide_Ubuntu.htm" for step-by-step instructions. Just read it and do what it says.
To start the install, just go to these folders, open a terminal and start the files with sudo: "XeroxPhaser3100-1.0-linux-2.6Ubuntu-intel/setup" and "XeroxPhaser3100sc-1.0-linux-2.6Ubuntu-intel/setup"
1. For this purpose, it's easier if you always choose the GUI step, rather than the terminal commands.
2. The cups server pages on your machine will look completely different from that in the instruction, but you will find what you need (add printer, configure printer, things like that)
3. Virtualbox: You do not need any special setting to scan in there. Just make sure you use the full version which has USB support (see the virtualbox website), and not Virtualbox OSE from the repositories.