Can't see co-located website from within lan

[Stev]

I have set up a DNS server (BIND 9.2) to resolve names on my lan. It seems to work great except I cannot resolve the name of my companies website, which is co-located elsewhere, nor can I connect using the IP address. In other words, I can resolve my_server.mydomain.com that is a machine on my lan, but I get DNS errors on

http://www.mydomain.com.

I have an entry in my configuration file for this machine, ie.
mail A 192.168.0.2
my-server A 192.168.0.3
chiron A 192.168.0.4
mail2 A 192.168.0.5
www A 123.456.789.123 (external ip address). I also have a forward first statement in named.conf to do external lookups first.

Any ideas?
Thanks in advance.