this is only a guide and should be taken with a grain of salt all routers are different and it took me like 20 mins to find the menu anyway and all menus will look different i have a b/g linksys wireless access point/cat 4 port 5e router
First you need to configure your router to allow port forwarding so yor server can connect to other computers and they can "see" you.
to do this, open a web browser and type 192.168.1.1 in the url
type admin in the password place adn press ok
a colorful webpage about your router should come up
now you should see a button called port forwarding somewhere, it may take a while to find or you may have to look in menus for it.
you should see a few rows and columbs of textboxes
in port forwarding,you wull need to fill in only 2 columns to get it working
application name: 1st one" hlds or whatever you want
2nd one: hlds or whatever you want
start: 1st one: 27000
2nd one: 1200
End: 1st one: 27040
2nd one: 1200
Protocol: 1st one: Both
2nd one: TCP
Ip address: both: 192.168.1.103
enable: both: check the checkbox