I had the same problem, emailed Tech Support and was sent to the following URL:
http://kbase.nemetschek.net/index.php?ToDo=view&questId=80&catId=21
Since all products come on the 3CDs, and since it appears that the other components of the LANDMARK product are on CD 3, it is not needed. Below is the excerpt from the above URL:
Depending on the products you have purchased, the VectorWorks 12 installtion may not require the use of all 3 of the shipped installation CDs.
Most of the installation process can be completed by CD 1. The components of the RenderWorks package are installed from CD 2 and some additional components of the LANDMARK product are installed from CD 3.
Note: This applies to Windows users. Installation on the Mac will require the user to insert all 3 CDs, regardless of the enabled products.
Hope this helps. It did for me
