10.3 Server VPN and Windows XP Clients

I have had a very difficult time connecting my Windows XP clients to the 10.3 VPN server from the Internet. Inside my LAN I can connect to the VPN from my Windows XP machines without a problem. When I try to connect from home, though, I have problems. Here are some details:

1. My XServe is connected to the Cable Modem through only a Gigabit switch. The switch’s only purpose is to amplify the Ethernet signal. When connecting the XServe directly to the modem (they are 300 feet away) I do not get a good connection.

2. I have enabled L2TP and PPTP on the OSX Server.

3. Inside the LAN I can connect via L2TP only from both my Mac OS 10.3 clients and Windows XP clients.

4. PPTP does not work anywhere for either my 10.3 clients or my Windows XP clients.

5. From the Internet my 10.3 clients can connect via L2TP. My Windows XP clients cannot.

6. I have opened UDP ports 1701, 4500, and 500 on the Windows XP clients (Windows Personal Firewall).

7. I have tried opening those same UDP ports on the 10.3 server.

8. I have tried applying the registry DVALUE for NAT-T traversal as described in the Microsoft Knowledgebase Article.

9. I have tried using TheGreenBow VPN client on the Windows XP clients. No luck.

I have been at this for months now, and feel as if there should be a solution. I keep hearing of people getting this to work. I would settle for PPTP, but that doesn’t seem to work at all! Help me, Obi Won Kenobi, you’re my only hope!