This is a simple step by step walk through on how to install Mono-Develop 1.0 in Ubuntu Hardy Heron. As usual I take no responsibility whatsoever on anything that may or may not go wrong.

Step 1: Open Synaptic Package Manager
Step 2: Search: Mono
Step 3: Select Monodevelop from the list to install.
Step 4: Click Apply.

That is all you need to do.