Install Zentyal from USB memory
First of all you need to download the ISO image on your HD.
It's recommended to check the MD5 sum to verify the ISO has been downloaded without errors.
Once you have downloaded the ISO file, insert the USB stick and launch usb-creatork-gtk (sudo apt-get install usb-creator-gtk if you don't have it already) and select the downloaded file
Please follow the instructions detailed for Windows clients here
Reboot and choose the USB media in the BIOS/EFI menu at startup.