I had similar trouble. I was able to connect to my LAN and get out on the net to upgrade the PS3 (in the settings menu), but could not connect to the PS3 Store. I turned the 6100's firewall down to "low" and was able to connect. Unfortunately, I can't figure out how to configure the firewall to let me through. For now I turn it down to access the PS3 store and turn the firewall back up when I'm done.
I have the same basic issue when trying to FTP my web site to my web page server.
Anyone out there know how to setup rules for the Westell 6100 modem/router?