IPV6 support on Win2K3

Currently we are planning to port our IPv4 based application running on
Win2k3 (IPv4 stack) to IPv6.
We came to know that Windows Vista onwards there is a new mechanism where in
a single socket can be used for both IPv4 and IPv6 (WSK, Winsock Kernel). But
since our application is running on Win2K3,
* is there any way the single socket option can be implemented in Win2K3
with Winsock2 API.
* Is there any driver which I can install to provide this functionality ?
* Currently we are planning to use following options if stack/winsock does
not support single socket
- Create multiple socket (we want to avoid this if possible)
- Create separate thread for IPv6 and create dedicated socket for IPv6
- Use two separate sockets and non blocking select API
Any comment on this mechansim ? Or any other alternatives?
* Also is there any plan to port WSK APIs to Win2K3 or support IPV6_V6ONLY
to use a single socket .

Appreciate inputs on this.