Switching between DNS addresses easily

You could use the netsh.exe command-line utility to achieve that. I found this page which provides some examples, including a couple to edit nameservers.

I use Net Profiles for this purpose. You can make predefined network profiles and easily switch between them at any time:

Features

• Save your network settings as profiles.
• Automatically activate wireless profiles when specified wireless connections are detected. (XP only)
• Change IP Address, Subnet Mask, Default Gateway, Primary and Secondary DNS Servers, WINS Server, and DHCP settings with the click of a button.
• Specifiy different mapped drives for each profile.
• Change your default printer based on which profile you're currently using.
• Automatically change your profile via program shortcuts created with Net Profiles.
• Change the default homepage for Internet Explorer, Firefox, and Opera.
• Proxy settings for Internet Explorer, Firefox, and Opera.
• Run a user-defined list of programs when a profile is activated.
• Maintain seperate desktop wallper for each profile.
• Change screen resolutions and color quality when profiles are activated.
• Can be easily translated into other languages using the enclosed XML language file.

Net Profiles is free and open source.