You'll find the DNS servers in the router's status page, where it tells you a summary of your connection. These should be the same as what your internet provider gave so if you can't find them you could always phone your net provider and ask their tech support.
To set up a custom IP address for your PS3 look for DHCP in the router settings. You will need to use the PS3's MAC Address to do this - go to Settings, then System Settings, then System Information to find this on the PS3.