DHCP Dropped connection or Losing route to host

Hello,

I have a problem with what I think is DHCP leases where a workstation
will lose it's ability to communicate with our internal DNS server to
resolve internal hostnames and attempts to resolve the hostname
externally but this cannot be done as it tries to go out through our
firewall and back in. I was told by my firewall provider that this
was not allowed.

Servers running Windows 2000 SP4 Active Directory and workstations
running XP Pro SP1.

Any help is greatly appreciated!

Thanks!