I have the same problem, of course, I'm behind a router, so I need to setup port forwarding to get it to work. First off, you need a domain name, if you want something free, I suggest
www.ath.cx Now setup for a static or dynamic IP address, you can have anything like
http://getlost.ath.cx and so forth, it must end with one of their endings unfortunately

but eh, you get what you pay for hehe
It'll then find your IP addres for you, and unless places like your ISP block port 80, you shouldn't have a problem
(I'm starting to feel so smart now :P great for meh self esteam

)