Question : VPN DNS Alternate DNS Server Configuration in Windows XP

I have a user that has a DNS server IP address they use at their office, but when they go home, the computer needs to automatically discover their ISP's DNS server. They don't want to have to go to Lan Properties>TCP/IP>  and change the server address to "automatic" every time they go home, and switch it back when they come back in the office. How do we configure his network setup so that it will use our dns server in the office, but auto-discover their ISP's server at home?

Answer : VPN DNS Alternate DNS Server Configuration in Windows XP

I would setup dhcp on his router/firewall to hand out your dns server as primary and the isp dns-server as secondary
That way even if the vpn tunnel collapses, he still uses the secondary for internet usage.