I know this sounds stupid, and you probably already made sure of this. The default functionality of the Linksys router is to dole out IPs based on DHCP requests. Make sure your host is on a static IP and your port forwarding is set for that IP. My TWGS and Website are behind my Linksys router and they are happy now that they are both static IPs. It sounds stupid to suggest something so trivial, but if your used to connecting to "Localhost" or 127.0.0.1 and it works, then you probably dont realize that your IP has changed via DHCP and your port forwarding no longer works. Just a suggestion, probably not it but I thought I would try. [:D]
Also, make sure under port forwarding that you have it set on "BOTH" under forwarding (not just IP or UDP). Another stupid one is make sure your forwarding the right port to the right machine. Dont send port 80 to you TWGS and port 21 to your web server.
Make sure if you are not using DHCP that you have set up the correct DNS and GATEWAY information under TCP/IP properties under Network Properties in windows. The gateway IP being very important, its probably X.X.1.1 where that X's are whatever IP range you have in the router (most likely 192.168.1.1).
Make sure TWGS is stup for "Automatic" under the IP properties. It will most likely be the internal IP address of the server its on, but I have mine set to automatic and it works fine.
If you have CABLE MODEM service (such as Cox High Speed Internet (HSI)) then DROP YOUR SERVICE IMMEDIATLY!! I had so much trouble with my website and TWGS going down, locking up, not accessable, slow throughput, etc. when I had cable modem service. The instant I changed over from cable to business class DSL my problems were over with no other changes made on my end. ($10 more a month, but WELL WORTH IT!)
Another stupid one, but might as well take a look is if your using some kind of Dynamic Domain Name hosting such as dyndns.org then make sure your public IP you got when you connected to the internet is the one reflected in the dyndns.org database. you need to update that everytime you change IPs.
Hope one of those things helps. If not, drop me an email and I will be happy to help walk through your settings and make sure they are all A.O.K.