After you install Interiorcad, run Vectorworks and ensure that:
1) You are in the Interiorcad Workspace by going to the menu:
Tools > Workspaces
and choosing an interiorcad workspace.
2) Then go to the menu:
interiorcad > Settings > Preferences...
3) You will be asked if you would like to use interiorcad in metric or imperial. Make your choice.
4) Interiorcad will update some libraries, then present you with a dialog box where you can enter your Activation Code:
[ Please make sure that you are entering the Activation Code for the version of Interiorcad ("XS" or "Full") that you installed, and that you are using the Interiorcad Activation Code that is assigned to your Vectorworks serial number. Activation Codes for other Vectorworks serial numbers will not work. ]
5) Press the "OK" button and you will be taken to the Interiorcad Preferences to begin working.
You're ready to go!