If you are running out of the box, you are using port 8080 at address 0.0.0.0 which means that GWAN is listening at all addresses.
So if you are running the browser inside the virtualbox machine why don't you try 127.0.0.1:8080/?hello.c
If you are running the browser outside the virtualbox machine, then it could be a network configuration problem.
Check out the FAQs of http://www.gwan.com/faq they give great information regarding installation and general problems.