it's very annoyed me if my client during remote area was got different DNS ip address rather than my corporate IP address. usually I change on the fly on my Linux Box but in Microsoft base My user need to redial PPP connection to activate new DNS name.
Herewith what I'v Done in windows 7 to change ip address setting including DNS on thefly.
netsh interface ip set dns name="Local Area Connection" source=static addr=none
netsh interface ip add dns name="Local Area Connection" addr=192.168.0.24 index=1
netsh interface ip add dns name="Local Area Connection" addr=10.1.1.21 index=2
netsh interface ip set dns name="Local Area Connection" source=dhcp