The accountants were having trouble accessing an IPv6 file share on their Vista machines, but their 2003 server and my Ubuntu Linux box could access it just fine: this condition developed over the weekend. The DNS functionality on the 2003 box is suspect, and we're looking to replace the box: in the meanwhile, I did some digging to figure out what was going on. A run of Wireshark yielded that when you plugin a network cable into a Vista/7 box, you generate LLMNR broadcasts on UDP port 5355. I set the firewall on the server to unblock that port on the local subnets and rebooted it: the Vista clients were able to access the share afterwards. Coincidence perhaps, but definitely something to keep in mind when managing DNS-based stuff.
Microsoft documentation on LLMNR
btw, if you want to route an IPv6 share to an XP or 2003 box, you can setup a portproxy to map port 445 of the target server to any unused local port. Example...
netsh int portproxy add v4tov6 listenport=2000 connectaddress=servername connectport=445
As long as the servername has an AAAA DNS record and accessible over IPv6, it should work.