There is an easier way to install Mono, Monodevelop and gtk#. Go to the Mono Website listed below and download the self installing binary for linux called
mono-1.1.8.3_1-installer.bin
http://www.mono-project.com/Downloads
These are the steps you will need to do install it.
1. Open up a terminal (Xterm, Konsole, Gnome-Terminal)
2. Make the file executable by typing and running the following command.
chmod u+x mono-1.1.8.3_1-installer.bin
3. As root run the file by typing ./mono-1.1.8.3_1-installer.bin
This will walk you throug an install wizard.
Note you need to be root or at least use the sudo command when running the wizard as it needs permission to install the files to the /opt directory.
Hope this helps
Regards
Scott