this may be a silly question, but I do not know if there is any special requirement o detail that force me to start a project following CS v4 instead CS 2009. Is CS 2009 obsolete? I know it is recommended to start as soon as possible with CS v4, but is there a critical reason for it?

We have a client that thought in CS 2009 and we do not know if, when CS v4 is already working, if it is possible to start the registration with CS2009.

Thank you in advance and sunny regards.