To be honest i'm surprised you can get it actually working with a Windows-xp machine doing routing…
To enable TCP/IP Forwarding in Windows XP, you just need to enable a setting in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
IPEnableRouter = 1
For more information on it, please check out the following links:
http://www.home-network-help.com/ip-forwarding.html
http://support.microsoft.com/kb/315236
Try setting the "Bypass firewall rules for traffic on the same interface" option under system–>advanced
Has definitely already been enabled, as it will not let me ping remote hosts at all without that option enabled.
But if you have 2 pfSense's on both side i would just stick to let the two do the routing.
I have one minor issue when using two pfsense devices for a direct site-to-site connection. I will get a post ready for those items.
Thanks for checking in with your input. It is much appreciated!