To put it simple, since you aren't using the same internet connection for both, you'll need to make a lag switch... or if you do have a router that wireless, or just an extra cord, plug your laptop into the connection shared with the PS3, use speed test or upload a ~10 min video to youtube and you'll have a good chance of getting host. It won't always work though, my parents usually have movies downloading while I play and it doesn't affect me much, my nets too fast