oops, pressed the submit button too early.

meant to say thanks for all the help - I've pasted the details into our intinerary.

Probably a bit late but I'd also mention Cerveteri which we visited on a trip early Feb 2007. It is a really amazing Etruscan site, tombs you can go into, like a buried town.
That same trip we also stayed in Viterbo and from there visited Orvieto and Villa Lante gardens at Bagnaia. We preferred Orvieto to Viterbo. Ostia Antica is the simplest to visit from Rome though, and is fantastic.