Apparently, you can install Ubuntu through a USB stick if your BIOS can boot from USB. I though this was pretty neat and wouldn't have to deal with throwaway media like CDs and DVDs. Unfortunately, each time I tried, the computer would not boot from the USB. It just kept booting from the harddrive no matter what I did in the BIOS.
I finally managed to figure this one out. The first 2 computers just didn't boot from USB. No hints. Nothing. Googling this problem brought up nothing. The solutions were to re-download Ubuntu, check your USB, use a CD, try on another computer, etc.
Fortunately, the 3rd computer I used gave me "Missing Operating System". Bingo! I found something searchable. This brought up a nice blog article. A solution! And it works! Basically, the problem was in the creation of the bootable USB. I was using Ubuntu's Startup Disk Creator. Apparently, it doesn't properly wipe out the USB and repartition appropriately. This caused havoc. The idea is to wipe out the USB stick and repartition before using Startup Disk Creator. This solved my problem.
Check out the solution here: http://ubuntuliving.blogspot.com/2008/11/missing-operating-system-step-by-step.html