Not quite sure what you are asking, are you only able to do the trip if you can use AA miles? If so, I would get back to them and ask how close they can get you to either Athens or Zagreb, then price the cost of completing the trip on intra-European carriers. Look at the budget carriers, good prices but added costs for luggage. www.whichbudget.com

It's possible that your difficulty in using miles may be because AA's parent company filed today for bankruptcy protection.

Can't help on credit cards as I don't live in the Staes but someone else will answer that.

I suspect British Airways flies to both, but sometimes it's easier to get seats on Iberia. Basically you have to fly into Madrid or London. An alternative would be to fly BA all the way to Athens and then use a budget carrier to get back to London from Zagreb (though in that case you'd probably have to go through Gatwick and then transfer back to Heathrow for your flight back to the U.S. I don't think this is a very difficult route, but some flights to and from Zagreb may be seasonal.

Carolina...alert! AA declared bankruptcy today...filing for Chapter 11..suggest you call. Article on AOL News/Huffington Post..

http://www.huffingtonpost.com/2011/11/29/american-airlines-bankruptcy_n_1118197.html?icid=maing-grid10%7Chtmlws-main-bb%7Cdl12%7Csec1_lnk3%7C116187

AA's statement on its bankruptcy filing indicates that it is committed to preserving the miles and mileage status of its customers. Basically, AA is trying to get out of some labor contracts and plane leases.

Beware flying BA on a mileage award - the airline does tricky accounting on its fares by reducing the cost for a seat on the flight (the "ticket price") but tacking on numerous fees. The most oppressive is the FUEL usage allocation. Most airlines incorporate the cost of fuel per passenger into the ticket price and may tack on a surcharge if the price of fuel goes up. BA separates the basic per passenger fuel cost from the ticket price and charges it as a fee for awards travelers too. That makes an award on BA more expensive to use than an award on AA. No clue if Iberia does this too.

The AA bankruptcy is irrelevant to this OP and shouldn't be a concern. But the point about fuel surcharges on BA (not to mention taxes) are well-founded. Your "free" ticket isn't going to be free at all.

I was able to secure an AA flight to Heathrow,and now I need one from Heathrow to Athens,AND then 2 weeks later from Zagreb to Heathrow.Any suggestions on how to do this in an affordable way????Thank you so much for your concern,all of you.

You should be able to use AA miles to connect in London onto BA to Athens. Failing that, use whichbudget.com and skyscanner.net to look for budget flights to Athens. You may need to change airports, most budget carriers avoid LHR. Each of the London airports has a website with info on how to transfer, although the easiest transfer is LHR to Gatwick. NOTE: there are extra costs associated with budget airlines, such as fees for paying by credit card, and be careful about luggage allowances.

If I were doing this I would look for an open-jaw FF itinerary into Athens and out of Budapest - you can reach Budapest by train from Zagreb.

You will get better advice if you re-post on the Airlines board) use the change forum tab).

You can also now use AA miles on British Airways from the US. (You didn't used to be able to.) There are 20 partner airlines with AA of which British Airways, Iberia and Malev (the Hungarian airline) may be helpful for your trip. You will have to phone AA to include those partner airlines in your search. You can't do it online. For example you can fly AA from DC to JFK, Malev from JFK to Budapest and Malev from Budapest to Athens. And Malev flies back to Budapest from Zagreb too! To do this kind of search I use www.kayak.com. Put in your details to search for the flights, then when the results are complete, look down the left hand side where all the airlines are checked that fly those routes. Just at the bottom of that list are little labels for "star alliance" (that's United) "sky team" (that's Delta) or "one world" (that's AA). Click on "one world" to narrow the flights to AA and it's partners. It of course is not telling you that award seats are actually available but it gives you different ideas of how you might do it so that then when you phone AA you can ask them "what about from DC to JFK and then on Malev through Budapest?"

Yes, you need to book flights on British Airways.

The easiest London airport transfer is Heathrow to Gatwick - that's true. But it's by default. The transfer sucks. Almost makes LaGuardia to JFK pleasant.

Any of the others (Heathrow to Luton/City/Stansted) are worse.

And the real killer for intra-Europe flights starting from Heathrow are the departure fees, I think.

Have you booked the award travel? If not (or if the change will be minimal cost), get a HOLD on it (good for 72 hours) and see what you can wrangle with Malev or Iberia through AA.

Also Croatia Airlines flies to Heathrow from Zagreb (and reverse). Keep that in mind. None of the Balkan airlines go intercontinental. See airlineroutemaps.com

"The transfer sucks."

Really? A non-stop coach ride sucks? What exactly do you want?

You mean you enjoy "non-stop coach rides"? The sort that are stuck in traffic as you see your checkin deadline get closer and closer?

I always allow lots of time for connections.. I've done the LHR to LGW or vv. coach ride a couple of times with no traffic jams, although there's always that possibility. And it's certainly simple.