No worries. Make a new folder on your desktop and call it HFM. Download the HFM.zip file http://code.google.com/p/hfm-net/
and extract it into the HFM folder you created on the desktop. Do this by right clicking on the zip file and opening it in Archive Manager. Once the files are in there, open up your terminal and type cd /home/your user name/Desktop/HFM obviously replacing your user name with whatever your user name is.
Now, in the terminal copy this into it sudo apt-get install mono-complete then it will ask you for your password and answer Y to anything it asks. Once that is done type mono HFM.exe and it will start up.
To open it up after you close it just navigate to the HFM folder again cd /home/your user name/Desktop/HFM and type mono HFM.exe to start it again.