Whos the Admin of the linux box? They or you need to configure the built in firewall if it has one configured (iptables, ipfilter or whatever) to allow tcp port 8000 and 8001 into the linux box.
If you are not familure with linux, switch to windows (blech!), no dont do that ! I was kidding.
If you have a router that uses NAT, how do you know its forwarding correctly? You must forward to the shoutcast server, not 127.0.0.1 or something address. If must be the IP address of the shoutcast box (linux), issue the command ifconfig -a |more to determine the linux box ip address, and make sure your router is pointing to that address as well.
You can verify if you have the ports forwarded correctly, but going to http://www.canyouseeme.org,
and putting in 8000 for the port to test.