IPHostEntry GetHostEntry IPv6 or IPv4 ?

I've been using the following code to return an IP (v4) from a host name. However, this doesn't work on Vista IPv6 address returns.

Q. How can I change this code to detect the OS and find the IP per Host name accordingly?

        private IPAddress GetIP()
        {
            IPAddress thisIp = null;

            string strHostName = Dns.GetHostName();
            IPHostEntry iphostentry = Dns.GetHostEntry(strHostName);// Find host name

            foreach (IPAddress ipAddress in iphostentry.AddressList)// Grab the first IP addresses
            {
                thisIp = ipAddress;
            }
            return thisIp;
        }