The installer will not recognise 32-bit installs of Cubase or Nuendo on 64 bit version of Windows (XP or Vista), therefore in this case you have to install the Cubase Automap client manually by placing it in:

C:Program FilesSteinberg[your cubase version]Components

Please go to this article to download the files.

Note that 64-bit Cubase and Nuendo are only supported on Vista X64, not XP X64.