IMPORTANT: Dropbox will sync everything you have to your EC2 machine, so if you are already using Dropbox for a lot of stuff, you might want to create a separate Dropbox account just for the course.
Start at the login prompt on your EC2 machine:
cd /root
Then, grab the latest dropbox installation package for Linux:
wget -O dropbox.tar.gz "http://www.dropbox.com/download/?plat=lnx.x86_64"
Unpack it:
tar -xvzf dropbox.tar.gz
Make the Dropbox directory on /mnt and link it in:
mkdir /mnt/Dropbox
ln -fs /mnt/Dropbox /root
and then run it:
~/.dropbox-dist/dropboxd &
When you get a message saying “this client is not linked to any account”, copy/paste the URL into browser and go log in. Voila!