The FC4 kernel already supports IPv6, you don't have to do anything there.
In FC4 do the following:
Start the network configuration tool. If you cannot find it in the menu, you can launch it from a command console with
Code:
system-config-network
Double click the interface for which you want to enable IPv6.
In the "General" tab, check the "Enable IPv6 configuration for this interface"
Accept your changes.
Done!