There are privacy issues abounds related to the Windows 7 implementation of IPv6. I won't get into them here, I'm assuming if you're reading this page, you are aware of these issues and wish to disable it.
If you need a desk reference for tweaking Windows 7, consider Windows 7 Tweaks: A Comprehensive Guide. It's a lot better than the O'Reilly Windows 7 book, and it's cheaper too.
(NOTE: You must be logged in as a Administrator to make these changes.)
To Disable IPv6 stack:
1. Open the Registry Editor. (Start -> type "regedit" in search box)
2. Find the following key:
4. Enter the following in the resulting window:
Some web pages say you should enter a "0" here, but that actually will enable IPv6.
To Disable Teredo Tunneling Protocol:
1. Click Start -> Control Panel
2. Click System and Security
3. Click Device Manager (the UAC prompt will appear, click OK)
4. In the Device Manager Windows, click View -> Show Hidden Devices
5. Find the Teredo Tunneling Pseudo-Interface in Network Adapters
6. Right-click Teredo Tunneling Pseudo-Interface, and select Disable.