After downloading Ubuntu.img to external drive can I set computer to boot from that drive?

"AFAIK, no. You should create a bootable usb drive.

There's a great project for this. Is called unetbootin. With a simple graphical interface, you select your img and the program itself creates this bootable usb drive.

It works. I tested in my hp latop running Windows Vista. I use it as a ""live cd"" alternative."