Whenever I turn on my PS3 or quit out of a game on it everything that is on the wireless network is kicked off then after a few minutes or so everything signs back on.
Do you have a Linksys WRT54G? That's the exact same problem I had FOREVER. Hold on and I'll find you the forum post I followed to fix it.
Edit: Never mind I remembered what fixed it. Try disabling your UPnP, that's what worked for me. I also found some places that said to update the firmware on the router.