You got an answer in Solution 1, but this is not a really right way with Ubuntu. You need to go for installation manager (like Synaptic, http://en.wikipedia.org/wiki/Synaptic_%28software%29
]) and search for Mono. If you want to do development, I would recommend to start with MonoDevelop (http://en.wikipedia.org/wiki/MonoDevelop
]). In this way, MonoDevelop will be installed with all dependencies, and with Mono, of course.