Following an online tutorial that uses an object named "icosahedron" from Add > Mesh > Regular Solids > Archimedean > Icosahedron. This object is not available in my version of Blender (2.74). Presenter asks me to include an add-on named "Add Mesh: Regular Solids", which again is not listed in my User Preferences dialog. What can I do about it?
The plugin you need is called now add_mesh_extra_objects. To enable it press CtrlAltU to open the preferences window. On the Addons tab type extra and and check the box for Add Mesh:Extra Objects
There are new options on the add mesh menu. Select Math Function Solid.
On the tools tab (T) select Icosahedron
Alternatively press F6 to access the option for the tool.