R – Checking MVC.net is installed from Web Setup Project

The installer variable for the Virtual Directory is TARGETVDIR.

It is possible:

Right-click on the setup project, and choose View->Registry from the context menu.
Right-click on HKEY_Local_Machine, add a new key, call it Software.
Right click on Software, add a new key, call it "MyCompanyName".
Right click on MyCompanyName, from the context-menu, choose new->String call it installation folder.
Left click on the installationFolder key, and set property value to [TARGETDIR]
Add an additional string key, call it version and give it the value [ProductVersion]

including the []

On x64, you'll find your registry key in regedit under
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\YourCompany]

But programmatically, you can read it normally, from normal projects and web projects, with:
My.Computer.Registry.GetValue("HKEY_CURRENT_USER\Software\YourCompanyName", "Installation Folder", Nothing)