Disappearing Nero Showtime Option During Setup

I tried to install Nero Express 7 and Nero Showtime 3 from the Nero 7 Essentials 7.9.6.4 CD of my new optical drive but during setup there is no option to select Nero Showtime in custom setup as shown. But, the same CD can be used to install Nero Showtime in the retail shop. This really baffles me as my computer has Intel Core 2 Duo 1.66 GHz processor wth 1GB RAM and 20GB free disk space. The requirement to install Nero Express Essentials is only Intel Pentium III 1 GHz processor with minimum 256MB RAM and 1GB free disk space.