Iptables is actually a collection of 3 or more filters or tables - INPUT, FORWARD and OUTPUT. For this, I'll assume it's an input to port 10000 you are looking for.
When you wish to specify a port number or range of ports, you must also specify a protocol - TCP, UDP, ICMP, ALL.
so the command line might look something like this:
iptables --append INPUT --protocol ALL --source-port 10000 --jump ACCEPT
Which reads "append the INPUT filter to ACCEPT ALL protocols with packets with which are destined for port 10000"
Hope this helps some