1.use 'fix mapping' function of the router to fix your ip address;(can also be done in Network Settings in your PC by manually inputing your ip, netmask, DNS; check these info by using 'ipconfig' under DOS)

2.use 'virtual server' function of the router to direct all the request for certain port to your ip.eg. set the 'service port' to be 2345, and service ip to your ip(set in step 1);

3.SAVE ALL SETTINGS, RESTART YOUR ROUTER(IMPORTANT STEP);the router address, say it is 218.202.23.45;

4.set up your server(whatever server it is) use your ip address(step 1) and port number(step 2);

5.the outside world can access your server by typing address like this: ftp://username:password@218.202.23.45:2345 for ftp(username:password optional,depend on your settings of the ftp);
and other ports for other services.

6.done.