In the advanced tab click on IPv6, select mode tunnel, configuration manual,
Server IPv4 address on tunnelbroker.net equals, remote IPv4 address on your Apple Time capsule
Server IPv6 address on tunnelbroker.net equals, remote IPv6 address on your Apple Time capsule
Client IPv6 address on tunnelbroker.net equals, local IPv6 address on your Apple Time capsule
Routed /64 on tunnelbroker.net equals, LAN IPv6 address on your Apple Time capsule
Hope this helps

Apple Time capsule firmware 7.4.2
One more thing, if you are assigned an ip via DHCP from your service provider you must set this manually!!! or-else it just won't work.
