equivent of /proc/sys/net/ipv4/ip_forward in windows

 # In Registry Editor, locate the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
# Set the following registry value:
Value Name: IPEnableRouter
Value type: REG_DWORD
Value Data: 1
A value of 1 enables TCP/IP forwarding for all network connections that are installed and used by this computer.


http://support.microsoft.com/kb/315236