Salut cher ami,
i had the same problem until i found out that if i use my router i cannot use port 80 for HFS - as the router uses port 80. So i had to use another port, actually port 7977.
When i want to see my files in HFS, i choose
http://192.168.1.33:7977 (33 depends of the router-type and is for the FIRST machine here, my other machines use 34, 35, and 36 - you have to look this in your router-manual), and my friends could go there by my external IP
http://externalIP:7977But i use a redirecting-service from DynDNS and from No-IP, which first hide my external ip-number and second offer by this a domain which is always the same after rebooting Windows.
For creating such a redirecting-service for No-IP i can send you my manual by e-mail.
Yves