DNS Resolution does not Shift When PPTP VPN Established

I have noticed a peculiarity when several Windows 2000 and Windows XP
Professional systems establish a PPTP VPN connection to an ISA 2004 Windows
2000 Server, while the TCP/IP properties appear to correctly list the
Intranet DNS server as the source for name resolution, the clients appear to
continue to send these queries to the Internet DNS resolver.

NSLOOKUP however, appears to correctly go to the intranet DNS. The problem
seems to affect all other utilities that have been examined, including: PING,
TRACERT, IE, Firefox, Opera, and the Terminal Services client.

Thoughts?