Stella,
As you're "first timers", my first suggestion would be to have a look at the Guidebook Europe Through The Back Door. That will provide lots of useful information to help both in travelling and with planning.
Given such a short time frame, you'll need to be somewhat selective and plan carefully! Which place to choose will depend largely on which is most important to both of you.
As others have mentioned, two days or so is usually good for Athens. Spending some time in the Greek Islands (Santorini?) would be a nice addition but that's going to add travel time. Given the geography, Greece is not as easy to travel as other places that have high speed rail lines. Spending at least half a day to get to Athens (if travelling from Rome) is probably not the most efficient use of travel time.
Italy is also a great choice, and you could easily spend two weeks exploring there. I'd suggest limiting your trip to Rome and the north of Italy this time. If you have a PBS TV station in your area that shows Rick's shows, those may give you some ideas on places you might like to visit. Tuscany is always one of the more popular locations.
As someone else mentioned, London and Paris would be another good choice for a two week trip, but London especially tends to be a bit on the "pricey" side. Using open jaw flights would be best, so that you don't have to return to London for the flight home.
I'd probably start by making a list of the places you most want to see, arranged from "most important" to "least important". That will give you a starting point for your planning.
Good luck!