Vista - Vista Client won't get IPv6 address via DHCP

I have a virtual network with a W2K8 server and a Vista client, both on same
subnet, can ping each other via IPv4. Both running SP2.

The W2K8 server has a DHCP scope defined for IPv6 and should be handing out
addresses. The Vista client is configured to obtain an IPv6 address
automatically. I've also used the netsh command to make the following
changes at the client:

netsh int ipv6 set int 8 routerdiscovery=disabled
netsh int ipv6 set int 8 managedaddress=enabled

As far as I can tell, the Vista client should be asking for an address from
the DHCP server, however, IPCONFIG /ALL isn't listing any IPv6 addresses
other than the link-local unicast address of fe80...

I'm looking for the site-local address of fec0... to be received from the
DHCP server, but there's none listed.

I've ensured DHCP traffic is allowed in the firewall. Not sure what to try
next. I don't have any other clients, so I can't test others.

Thanks in advance!

are you sure you setup the server in stateless mode