Can't listen on other computers
 

I set my server up using the DNAS Gui, but I can only connect to the server on my computer, see I can't connect with this...

http://127.0.0.1:8000

I think I configured my server wrong.

That's your local IP, useless for connecting from outside, http://www.showmyip.com that's the IP you have to give them, for example: http://real-ip:Port/listen.pls

If you are sitting on the PC with shoutcast then you can use that address 127.0.0.1 or localhost. If you are on another PC on your own network use the internal LAN IP address of the PC with shoutcast. If you want your friends to listen then use the WAN IP address that you see in my signature.

Would that also work even if I'm uaing a Linksys router?

you need to forward the ports 8000 and 8001 in the router config.

see the sticky thread shoutcast FAQ there is a section about routers and your brand is named there or google for their website.
also read the manual that came with this router.