what is private IP addresses,and why are they used?
What does a "$" do to a shared folder name? Does this make it more
secure? Who has access by default to C$:?

Private Ip addresses are the blocks of IP addresses that are set aside
for use on private networks. These ip addresses are not accessible on
the global internet, therefore they can be used by any number of
organizations without conflicting with the general internet. By using
network address translation, workstations using any number of these
"private" ip addresses may share the same "public" ip address. Since
each public ip address can only be assigned to a single entity at any
given time, the private ip spaces were set aside for this purpose.

The ranges of these addresses are defined by what is known as "RFC
1918", and are as follows:

192.168.0.0-192.168.255.255
172.16.0.0-172.31.255.255
10.0.0.0-10.255.255.255

the $ at the end of a windows share indicates that it is not normally
shown to clients when browsing the shares on their computers. In order
to access such a share, a user must know about it ahead of time and
type it in as such:

\\computername\sharename$

This is an addded security feature to disuade the casual observer,
however there are programs such as cain and abel (www.oxid.it) and
X-scan that can find out exactly what shares are available regardless
of $ protection.

As for the default C$ shares, there are shares that windows makes
automatically for each drive on the computer. In order to access these
shares, one must normally log on to the computer with an account that
has administrative priveleges. I came accross one computer network
where no password was needed, however, this was probably because the
administrative password was blank or the "anonymous" user had
administrative priveleges. If neither of these are the case with your
computers, then only users with administrative priveleges on your
computer will be able to access these default shares.

I trust this adaquately answers your question and I hope you found
this information satisfactory.

Search Strategy: 
"private ip space"
"hidden windows shares"

Sources:
http://www.cites.uiuc.edu/guidelines/network/private_ip.html
http://is-it-true.org/nt/registry/rtips2.shtml
http://www.oxid.it

Private IP is an IP that is not routable on the internet.
Public IP is what you receive from the ISP, that is routable over the internet.

Reason: Public IP's cost money and are limited.

--

Hide ?Shared As? Names.  Windows does not broadcast ?shared as? names
ending in a dollar sign (e.g. ?Shared$?).  Consider hiding ?shared as?
names for resources containing sensitive information.  Hiding shared
resources comes at a cost, however, because legitimate users on a
local network cannot see the ?shared as? names, but drive mapping is a
workable substitute for local network users in most cases.



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