Moving Itunes 11 to a new PC?

Please can someone help?
I am NOT an Itunes person - I don't like it but...
I was asked to put some music onto an Ipod for a pensioner from their Tape and CD collection.
I ripped the CD's, Downloaded some extra MP3s, and transferred all his tapes to MP3 format.
I installed Itunes 11 and imported all this media and synced to his new Ipod.
All done and he is happy.
Now I would like to remove all this from my PC but before I do would like to "Back it all up" so that someone could, if he asked, restore this to another PC and add more media to it for him.
What approach should I take, the Backup to disk option is gone from Itunes11
Suggestions on the best method please.
Thanks