using filebox is the best way if you dont know the full command...

open filebox...go to where you downloaded the hildon desktop files...once you at that folder press the upper right icon...it will popup some menu...look at bottom left,you will see open terminal here...press it then x-term will open...
once x-term is open then just type this...

dpkg -i hildon-desktop_2.2.142-13_armel.deb

remember enable the root access on filebox first if you want it to works...