Check here:
LinkSys BEFSR41 for GSA and SFC NOTE: For port forwarding to work correctly, the client machine
must be configured with
a static IP address (I disable the dhcp server on the linksys too).
If running windows XP make sure that the firewall(s) are off, and that the
Internet Gateway Device Discovery and Control Client is installed and that
UPnP is not installed.
At the router, check that "Block WAN Request" is disabled and
disable all UPnP port forwarding and fill in the port forwarding table
as in the link above.
Under this configuration SFC2 will work, but SFC3 will need to be informed of the WAN IP address
unser the [Meta] section of the SFC.ini (IPAddress = XXX.XXX.XXX.XXX).
Hope that helps...