oh my GOSH! what huge (and happy) news!!
congratulations!!
what kinds of things are you looking for to calm your nerves? yoga and deep breathing exercises can help quite a bit (but check with your doc before taking on the yoga)..... prenatal massage can also be a huge help -- just make sure that you find someone who is actually licensed in prenatal work.
We have a couple articles and videos on the site that cover both topics, so it might be worth peeking at. Let me know if you want links and I'll get them to you.
We also have a blossoming community of twin mommies on our BabyTV message boards -- there are some great women over there who have seen and done it all, so you might want to try posting there for some really great advice from seasoned pros. (And, you can log in there using the same log in that you have here, so you don't have to register for another site or anything like that). Here's the link:
http://www.babytv.com/Community/forums/31.aspx
-m