The most likely reason is that both the laptop and the PS3 are using the same IP address.
Easiest way to handle it is to make sure the router is acting as a DHCP server (assigning dynamic IP addresses) and the PS3 and the laptop are set as DHCP clients.
Basically, you don't want to have any static IP addresses.
Also, make sure no one else can get on your wireless network you'll want to change the default password on your router and enable encryption.
(there are other measures you can take too to make your wirelss network secure... like enable the wireless MAC filter and disable the SSID broadcast)