Nominally ports 137, 138, and 139 (some of those used as UDP, some as TCP), but in practice other ports get used as well as negotiated endpoints for services located through the service lookup.
If you are lucky then the system communicates using SMB -- lucky in the sense that SMB network software source is available for study (see http://www.samba.org/)
When I was a network security admin, I had awful struggles to find out which ports were really being used and for what purposes. By the time I stopped looking, I had found ports being used for 21 different purposes, only 5 of those acting in accordance to documentation.
If you are running MS Windows, you might find it easier to Mex up some NETBIOS calls than to try to communicate directly with the device, especially since you would need to be listening on ports that MS Windows already thinks it should be listening on itself.