As you know, Windows does not support setting up DNS via Router Advertisements (RDNSS) for IPv6. So it should use a DHCPv6 server to somehow get the needed address.
I'm using DD-WRT on my router which have both DNSMasq as DHCP/DNS server (it supports both IPv4 and IPv6 it seems) and RADVD for router advertisements for IPv6.
The WAN is set up via DHCP with prefix delegation, and RADVD is handling the prefix delegation to the LAN. IPv6 basically works... Just DNS is not assigned on Windows machines.
How do I set up my system, so RADVD still distributes the addresses on LAN like it does now, and DNSMasq take care of handing out the DNS server for the IPv6 clients (so it would work with Windows this way)?