How to download Ubuntu without installing?
Solution 1:
Yes, it's possible. You didn't say if the computer where you will download runs Windows or Ubuntu. But you need to download the Ubuntu ISO on that computer, then prepare the memory card or USB stick, and finally boot the second computer using the stick or card.
Download Ubuntu from here: http://www.ubuntu.com/download/desktop/
See this guide on how to do it for Windows: http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-windows
and this one if your first computer runs Ubuntu: http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-ubuntu