you are correct, the English AIDA web site seems to be gone.
AIDA is now a part of Carnival Corporation, so if you are interested in booking an AIDA cruise, it might be a good idea to call Carnival Corp. to ask where this is possible for somebody living in the U.S.
Another possible contact would be Princess Cruises (now also part of Carnival Corp.). Seetours (the German Carnival affiliate which operates AIDA) also markets Princess in Germany, so this might be vice-versa.
Finally, if you send me your postal address by private mail, I will try to get an AIDA brochure for you. It's in German only, of course.
BTW From next April, AIDA will have a fourth ship "AIDAblu" - the former "A'Rosa Blu" / "Crown Princess". She's much larger than the rest of the fleet at more than 70,000 gt. Her summer 2004 deployment takes her to the Baltic, Norwegian Fjords and "Top of the World".
Hope this helps!