Test if Firewall is blocking a Port. Check which Ports are being used. Also learn how to check which process or service is using the open port.

I'm writting a server program, don't know how far I'll get but I'm giving it a try. What I need to do is open a new port for each user (connection). How, programaticly, do I check if a certain ...

You could try telneting to port 139 from an outside machine. If you get anything other than an access denied, you likely have an open port.