Go to your SME admin page, click hostnames & addresses and then CREATE A NEW HOSTNAME FOR A LOCAL HOST. Enter your Win2k server name and local IP. Then when your initiate a vpn session, you will be able to ping the win2k box.
e.g. ping win2k.yourdomain.com
or
ping win2k
If that doesn’t help, let me know and I'll send a howto on setting up vpn to the Win2K server. It's not as easy as adding portforwarding as you will need to forward an IP Protocol (Protocol id:47) as well.
Good luck.