"Ports" are completely arbitrary.  You can use any one you want as long as nobody else is already listening on it.  
In Sickbeard, if you go into Config then "Search Settings". 
SABnzbd URL: 
http://<bla address>:
8000/
The bold number has to match what you set in Newsbin. So, set Newsbin to 8100 and restart it.  Then change the Sab URL to 8100 too.  Use whatever address you already have in there. Only the port changes. 
SABnzbd URL: 
http://<bla address>:
8100/
After I restarted Newsbin this was what I see.  Newsbin is listening on 8100. 
PS C:\Windows\system32> netstat -ntb
Active Connections
  Proto  Local Address          Foreign Address        State
  TCP    192.168.10.153:8100    192.168.10.201:61531   TIME_WAIT
  TCP    192.168.10.153:8100    192.168.10.201:61532   TIME_WAIT
  TCP    192.168.10.153:8100    192.168.10.201:61533   ESTABLISHED
 [NewsbinPro.exe]
PS C:\Windows\system32>
You have to run a command prompt "As Administrator" to run this command. 
I'd disable "Remote Control" while testing this.