There's a great setup guide for Polycoms here:
http://www.sureteq.com/asterisk/polycom.htm
I wish I'd had that guide when I first set up my phones, it was a steep learning curve at first. Now that I'm running, though, it's great.
You may not need to do the section on setting up DHCP, but instead just manually configure the phones. When the phone first starts up, use the softkeys to enter configuration mode (the default admin password in a Polycom phone is 456) and enter the server address (the IP of your PiaF server) and set the mode to t*f*t*p. Use the rest of the guide to set up the configuration files, and you should be up and running pretty quickly.
Despite some information that states otherwise, you can even use Polycoms in NAT (address translation - meaning across the internet using a firewall on one or both ends) environments. You just have to open the firewall ports on the server end for SIP control (ports 5060-5082 UDP) and audio (10000-20000 UDP). When you add the extension in FreePBX on your PiaF server, make sure NAT is set to yes.
Jeremy
"Do or do not. There is no try." --Yoda