[Novalug] Basic security questions, NAT routers, LAMP

[John Christopher]

Hi -

I have the following:

- Laptop with Ubuntu Linux
- Verizon DSL connected with a Westell Wirespeed C90-36R516 ADSL modem
- Linksys WRT54G wifi router

I use the computer mainly for surfing, email, etc., but I am also
using it to learn web design and programming.

I don't know much about computer security, and I have several questions.

I have read that a NAT router is essential equipment to protect your
computer from attackers, etc.  Is the Linksys router a NAT router?

Is the Westell ADSL modem a NAT router?

Is NAT a feature that I must turn on, or is it always on?
Can it be turned off?

How can I tell if NAT is running / working?

I am also trying to learn web design and programming with LAMP
(Linux, Apache, MySQL, and PHP), and I want to prevent the Apache
and MySQL services from being visible to the world (I only want
to be able to access them on my laptop).

Are Apache and MySQL accessible to other computers thru the
Westell / Linksys?  If they are, how do I prevent this?

If I am connected to wifi away from home (airport, panera, etc),
are Apache and MySQL accessible to other computers?  If yes,
how do I prevent this?

How do I prevent my laptop from being vulnerable to attack while
using public wifi?  What commands do I type to determine if it
is vulnerable?

Thanks in advance.