If you arrive in Manhattan on the Staten Island ferry, how long a walk is it to the WTC site, and what subway would you take from there to Central Park/American Museum of Nat History?

This is a good site for planning subway journeys in NYC:

http://www.hopstop.com/

It's an easy 10 minute walk to the WTC site from the Staten Island Ferry.

In general, how difficult is it to walk around NYC? We're going there late July. Are things generally easy to find?

You can easily walk around, but it's a LOT of walking - you should plan to take the subway to the various areas and then get out and walk to explore.

is there an entrance to central park immediately close to the amnh?

Yes, right across the street on 81st and Central Park West.

what is the best way to do central park if you entered from there? any nice places to eat there?

In Central Park you could eat at The Boathouse; otherwise, there are tons of places on the Upper West Side right in that area.

Here is a nice virtual map of central park: http://www.centralparknyc.org/virtualpark
You will be right by strawberry fields when you enter the part - it is really pretty. I wouldn't eat at the boathouse - it is cool for the experience and the ambience, but the food isn't that great in my experience. Here's an awesome website to help find places to eat - you can search by neighborhood so you should be able to find something really close to the AMNH.
Have fun!
Casey

Sorry - forgot to paste the link to the restaurant website:
http://www.menupages.com/

Look for the B or the C train to the Museum. Both stop right at the Museum. (the A and the D are on the same line, but are both express trains and will not stop there).

New York is a walking city - and probably the best means of getting around and getting a real feel for the city. the only problemin July is the heat - which can be pleasant - or can be hideously hot and humid.

So - for shorter distances reco walking (unless it;s 95 and humid) and for longer the subway (fast, convenient, inexpensive and perfectly safe). For shorter distances and several people cab is also reasonable - if you can find one.

As for getting around the first step is to get a good, detailed streetmap. Once you're above about 12th St the city is set out on a grid pattern - with numbered streets as you move north (23rd or 34th to 59th is midtown, from 59th north is the park with the upper eawst or west sides on either side of it). Avenues are a mix of names and numbers - but - with a map it's a snap.

But - downtown is old New York - before the grid was designed and almost all streets have names - and since they were originally walking paths, often meet at angles.

The Ferry to WTC is not a bad walk. Up to Central Park and the Museum of Nat'l History is 4/5 miles - and subway is your best option. Therre are entrances to the Park everywhere - but the only place I would eat is the Boathouse. But - the area right around the museum has tons of good restaurants.

But - before you head into the park go to the web site of the Cenral Park Conservancy to get a map and decide which couple of things you want to see. (Central Park is larger then Monaco - more than 2.5 miles long.)

When walking around NYC, what should you generally carry? We'd like to have a camera and a map, as well as some room for souvenirs. Is a small backpack a problem, ie is pickpocketing a concern?

Lots of people wear small backpacks - but - on the subway and in crowds it's very easy to get things out of them - esp if you're not used to being on guard at every moment. (My stepdaughters sometimes use them - but they're New Yorkers - and have the sixth sense to manage them.)

You're much better off with a lightweight shoulder bag that you wear bandolier style across the chest - so you can see anyone trying to get into it.