Ok- I would suggest going into the router settings and set up a custom IP address just for the PS3. You will need the PS3's MAC Address for this (go to Settings, System Settings, System Information to find this on the PS3). Now, go into the router settings and look for DHCP (probably in the Advanced area). make the IP address high enough so it will not interfere with everything else, maybe make the last 3 numbers .110. Save that and then put that same IP address you made into your PS3's connection settings.
One other thing to try is find the DNS Server numbers as shown in the router's connection summary and enter those into the connection as well. The PS3 is a bit bad for trying to detect them automatically.