One issue I had with my router also a Linksys was that it forwarded to a set NAT based IP Address.
However the machine was getting the NAT IP Address via DHCP, which meant it changed on a regular basis, and so the port forwarding would soon stop working.
Unfortunately the router did not have a way of statically assigning an IP address to the machines MAC Address in the DHCP server.
I believe I could probably get around this by putting a different firmware on the device.
However as a quick solution I manually assigned an address to the computer that I knew would work and not cause interference with the DHCP Server.
A quick way to test that the forwarding has worked for the library server is by finding your external ip address using a site like
http://www.whatsmyip.org/and then typing the the external address into a browser with the forwarded port
so for example:
http://xx.xx.xx.xx:52199Where the xx.xx.xx.xx is your external IP. This should then open the web server's page up if there's a web page to connect to.