Build Instructions/Ubuntu-Mono-2.0.1
From OpenSimulator
First grab the normal stuff for the Mono
sudo apt-get install subversion nant libmono-microsoft8.0-cil libmono-system-runtime2.0-cil libgdiplus libmono-i18n2.0-cil libmono-oracle2.0-cil ruby
Then go to this website and read the compiling steps:
http://devarthur.blogspot.com/2008/10/compiling-mono-201-on-ubuntu-gutsy.html
PS: Be sure to use the ROOT user to compile, else it will fail