This is actually an old post from my personal blog. Since I have created this new blog dedicated to my technical life, I will gradually move my old notes to here.

Save this into a *.reg file

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"IPEnableRouter"=dword:00000001

then double click to import it into windows xp registry. This should be equivalent to doing this in Linux

echo 1 > /proc/sys/net/ipv4/ip_forward