1) Which Operating System is running the computer directly connected to the internet ? You have to route the port. With Windows NT/XP/2000/Vista there should be some network commands which allow you to set up that, look up "windows port forwarding" on google.
2) Set these vars :
set sv_allowdownload "1"
set sv_wwwDownload "1"
set cl_wwwDownload "1"
set sv_dlURL "http://your_http_repository_sorry_no_FTP_protocol"
But Hitman is right, check the wiki and google for these infos, they are not that hard to find.
Good luck