private network internals

[Bernd Prager]

I might embarrass myself by asking some trivial questions but I've been
trying to search online for weeks now
without finding a decent answer. Here I go:

I'm using Linux Debian/kernel 2.6.8 and bind9 9.3.1 connected via DSL to
the outside world.
I have one static IP address and bind is currently used as "cache only"
my provider's name servers.
All my internal boxes are running Windows provided with IP address and
host-name via DHCP 2.0 .
All internal boxes can properly resolve all external names. Now I have
one problem and one question:

The problem:
- My internal computer can't resolve any internal addresses e.g. stored
in /etc/hosts.
  Is this how a pure DNS cache is supposed to work? How do I fix that?
My question:
- How do I get DHCP provided host names for my internal computers in
DNS? I have no authority for my provider DNS
  (and I don't want my internal boxes to be exposed). This is entirely
for internal use only.
I read about dynamic DDNS and assume that's the way to go.
But I don't know how to mix read-only external zones with read-write
internal zones.
Any help would be greatly appreciated.

Thanks,
-- Bernd