Quick ADMX GPO policy to disable IP6 on your network according to MS KB 929852
IP6_disable.admx
IP6_disable.adml
Note The value "0" is the default setting.
2. Type 0xffffffff to disable all IPv6 components, except the IPv6 loopback interface. This value also configures Windows Vista to use Internet Protocol version 4 (IPv4) instead of IPv6 in prefix policies.
3. Type 0x20 to use IPv4 instead of IPv6 in prefix policies.
4. Type 0x10 to disable native IPv6 interfaces.
5. Type 0x01 to disable all tunnel IPv6 interfaces.
6. Type 0x11 to disable all IPv6 interfaces except for the IPv6 loopback interface.
http://support.microsoft.com/kb/929852