D.O. seems to have a lot of great tutorials for setting up webservers for multi-domain apache2/WordPress setups, but *none *for going from single domain to multi-domain.
I'm using one of the WordPress droplets to run ...
You could follow the steps from this video on how to host multiple WordPress websites on the same server with Apache Virtual Hosts:
[youtube iux5b7ZOKLg 320 560]
Essentially, what needs to happen is: