Configuration confusion

[Daniel Hogan]

Here is the scenario:

We are behind a firewall on a NATted network.  Our ISP has a DNS
server that is used to resolve names to their internal equilavent.  We
here at the office are on the same domain, but we are using our own
DNS with additional information.  I do not have any sort of access to
the ISP's DNS server other than just standard queries.  Is there a way
to set up BIND 9 so that if a query fails on our server  it is
forwarded to the ISP's server?

Translation:

ISP has the following names set up on their server:

someserver1.ispdomain.com
someserver2.ispdomain.com
someserver3.ispdomain.com

We have the following names:

myserver4.ispdomain.com
myserver5.ispdomain.com
myserver6.ispdomain.com


I want to be able to keep myserver4, myserver5, and myserver6
configuration only on our server, but be able to have our server ask
the ISP's server if anything else for ispdomain.com is asked.

Is this possible, and if so, how?

NOTE:  I have added someserver1, someserver2, etc. to our list as a
work-around, but the ISP likes to change their IPs every so often
throwing our copy off.

Thanks in advance.