Preliminary questions before installing Primary DNS server

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=20
=20
Primary DNS server for jerichoroad.net (Secondary DNS server for
xtechsolutions.net)
NetBSD 1.6.1 running BIND 9.2.3=20
-----------------------------------------------------
ADSL modem
Domain Name: xtechsolutions.net
External NIC: 216.206.233.187 (static)
Internal NIC: 10.0.0.1=20

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=20
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=20
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=20
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.=20
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.