What ports need to be open through a firewall to allow a NPM server and a remote poller to communicate. I looked in the manuals, but I didn't see the required ports.
NPM and the remote server should only be communicating on port 17777. The remote poller also connects to the DB directly, so you'll need to open that port as well.
Casey is right, please take a look at http://www.solarwinds.com/documentation/Orion/docs/OrionAdministratorGuide.pdf on page 13 is Orion Server Software Requirements section listing all required ports
You're right. I setup an additional poller today and used wireshark to verify what traffic was passed.
It's about 98% SQL calls from the additional poller to the database and 2% tcp/17777 traffic both to the main NPM server and to the additional poller.