Preliminary questions before installing Primary DNS server

[Keith]

Hi, I was hoping to setup 2 separate www, dns, and mail servers, and
have them serve as backups for each other. Here are the two machines
I've got to work with:

Primary DNS server for xtechsolutions.net  (Secondary DNS server for
jerichoroad.net)
NetBSD 1.6.1 running BIND 9.2.3
-----------------------------------------------------
  Cable modem
  Domain Name: xtechsolutions.net
  External NIC: 24.56.85.10  (static)
  Internal NIC:  192.168.1.1 
  
Primary DNS server for jerichoroad.net (Secondary DNS server for
xtechsolutions.net)
NetBSD 1.6.1 running BIND 9.2.3 
-----------------------------------------------------
  ADSL modem
  Domain Name: xtechsolutions.net
  External NIC: 216.206.233.187  (static)
  Internal NIC:  10.0.0.1 

I've read portions of Cricket's DNS & BIND, 4th ed, and the DNS & BIND
on NETBSD guide.  I worked through the example setup in the NetBSD
guide, and *think* I've got a fairly good handle on the configuration
files.  But I'm completely confused about where internal and external
addresses actually fit into things (which shows that I don't have a
fairly good handle on anything);)

If my hostname is xtechsolutions.net, and resolves to 24.56.85.10, to
what IP do I assign the name NS1.xtechsolutions.net (assuming the same
box is serving as web and dns server)?  192.168.1.1?  I don't even
know if I'm making my question clear, my background is serial
communications, not TCP/IP, so I may just be missing something very
silly.

In using the BIND and NAMED on NETBSD guide, the author uses the
following example:

--------------------------
Begin example
-------------------------
domain to delegate: example.com
primary dns server for example.com: ns.example.com
ns.example.com IP address: 10.0.0.1
secondary dns server for example.com: ns.other.com
ns.other.com IP address: 172.16.0.1

Here is how it is going to look like in the parent/name registry DNS
zone:
;
; Delegate example.com to ns.example.com DNS
;

Name       CLASS  TTL   TYPE  RR Data 
example.com     86400    IN NS ns.example.com
                86400    IN NS ns.other.com
ns.example.com  86400    IN A 10.0.0.1
ns.other.com    86400    IN A 10.0.0.2    (NOTE: why is this not
172.16.0.1?)

The last 2 lines are called glue records. Glue record is an A record
where the name appears on the right hand side of an NS record.
Here's the named.conf file taken from the example in the BIND & NAMED
on NETBSD guide.

------------------------------
End Example
------------------------------

I'm unclear as to whether to use my external IPs, which would
translate as:

domain to delegate: xtechsolutions.net
primary dns server for xtechsolutions.net: ns.xtechsolutions.net
ns.xtechsolutions.net IP address: 24.56.85.10
secondary dns server for xtechsolutions.net: ns.jerichoroad.net
ns.jerichoroad.net IP address: 216.206.233.187

Name                     CLASS  TTL   TYPE  RR Data 
xtechsolutions.net       86400    IN NS xtechsolutions.net
                         86400    IN NS ns.jerichoroad.net
ns.xtechsolutions.net    86400    IN A 24.56.85.10
ns.jerichoroad.net       86400    IN A 216.206.233.187    (NOTE: ???)

Or whether to use my external IPs, which would translate as:

domain to delegate: xtechsolutions.net
primary dns server for xtechsolutions.net: ns.xtechsolutions.net
ns.xtechsolutions.net IP address: 192.168.1.1
secondary dns server for xtechsolutions.net: ns.jerichoroad.net
ns.jerichoroad.net IP address: 10.0.0.1

Name       CLASS      TTL   TYPE  RR Data 
xtechsolutions.net    86400    IN NS xtechsolutions.net
                      86400    IN NS ns.jerichoroad.net
ns.xtechsolutions.net 86400    IN A 192.168.1.1
ns.jerichoroad.net    86400    IN A 10.0.0.1    (NOTE: ???)

I want to "get it", and I don't mind reading.  The docs I've read all
seem to use private network addresses and I just don't understand
what's going on.  I will be happy to provide config files, but I
thought it was pointless at this point.

I would have assumed that NS.xtechsolutions.net would have to be
assigned to an external IP (24.56.85.10) in order for it to be seen. 
Is it the case that as long as xtechsolutions.net is assigned to
24.56.85.10, any subdomains are also reachable?  I'm lost.

I also have read that since one of these boxes is fed by a cable
modem, I may have a problem with DNS.  If so, I think I can find
someone else to provide backup.  I do know that the ADSL provider
allows www, mail, dns server setup.

Any help (including directing me to further reading) would be
appreciated.