colette,
Congratulations, that's a wonderful Valentine's Day gift!
As you haven't been to Italy before, you may find it helpful to check your local Library or book stores to see if they have a copy of the Italy guidebook (you might consider buying a copy to use as reference on the trip). That will provide you with a lot of good information on all the places you're considering, and will help you to narrow down which places to visit and help with sightseeing.
As you only have a VERY short one week time frame and you're going to be jet lagged for the first few days, I'd suggest not trying to fit too many places in. Having a relaxed and enjoyable trip will provide better memories of this trip, and hopefully a desire to return.
Both Lago di Como and Lago Maggiore are beautiful and certainly worth a visit, but in this case I'd lean towards recommending Como and the small town of Varenna. It's a wonderful place to spend a day or two while you recover from jet lag. While there you could take a day trip to the posh resort of Bellagio or other locations in the mid-lake area. Who knows, maybe you'll see Clooney? I'm assuming you'll need directions on how to get there via train, and the group can provide those once you've made a decision on which lake to visit. I agree with a previous post that you should travel directly to the lake right after arrival.
For your second location, I'd suggest basing in Florence and taking at least one day trip. That will provide both a smaller location and a large city, to provide a look at each. It will also be easy to get back to Milan at the end of the trip for your flight home, as the trip to MXP will be 2H:41M (depending on which train you choose). Siena would be one choice for a day trip, as it's an easy connection from Florence via Bus.
As you've seen Under The Tuscan Sun numerous times, you're probably aware that the movie is set in Cortona. You could certainly substitute that for Siena and take a day trip there during the time you're staying in Florence. Be sure to leave some time to explore Florence as well, as there's LOTS to see! Travel time to Cortona is about 1.5H each way so it's easily possible. The group can provide more specific directions on how to get there if you need them.
One point to note is that the "real" Bramasole was not used in the film, so you may not be able to see it, but you can certainly visit the town. The house used in the movie is now a rentable Villa, I believe. Cortona was also used for the production of the Andre Rieu Tuscany concert, which is one of my favourites. You may enjoy watching THIS short video of the concert as it shows some of the Tuscan scenery, or THIS video which shows some views of the town of Cortona.
You'll need to be do some homework on using the rail system in Italy, and the potentially expensive "caveats" with that. If you need further information, post another note.
As May is not far away, I'd suggest getting some hotels booked SOON. That's spring shoulder season and it could be getting busy then.
Good luck with your planning!
