There was a special "Gardens of the World" on PBS hosted by Audrey Hepburn. I used to own it on video, but gave it to my sister. One of the segments focused on a garden outside of Rome that was built around streams and ruins. I wish I could remember the name of the garden. You can probaly find it a tyour local library. You might want to look at Feneschi gardens in Tuscany.

I just read further down the page and there's a posting on this garden. It's name is Ninfa.

Try the Villa d'Este in Tivoli outside of Rome.