If your WAN address is a /128 address, then you will need another subnet to use for your LAN. A major difference in IPv6 over IPv4 is that NAT is not intended to be used with IPv6 (there are so many addresses available, it isn't necessary).
If you're using SixXS, you should be able to request a subnet that you can use on your LAN. SixXS will most likely give you a /48 subnet, which is huge.
A good start for IPv6 info is the main wikipedia page:
http://en.wikipedia.org/wiki/IPv6 and also the IPv6 Addressing page:
http://en.wikipedia.org/wiki/IPv6_address.