These are the links I used.

Vatican Museum and the Sisitine Chapel.

http://biglietteriamusei.vatican.va/musei/tickets/do?
action=booking&codiceLivelloVisita=9&step=1

Borghese Gallery.

http://www.galleriaborghese.it/borghese/en/edefault.htm

Coliseum, Palatine and Forum ( all one ticket )

http://www.ticketclic.it/database/B2c__/order.cfm?siteDefID=170&LN=1

Plus we did 2 tours with walking Rome, book on line pay cash on the day.

Catacombs

http://walkingrome.com/tour.asp?idTour=2&idCatTour=1

Rome by night.

http://walkingrome.com/tour.asp?idTour=6&idCatTour=1

Hope that helps.

Regards

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