I am experiencing the exact same problem.
The weird thing is that this just started tonight. My PS3 has been working fine for a while, and it all of a sudden kills my network.
I'm not sure what the issue is, exactly.
I'm on my laptop at the moment. The wireless works fine when the PS3 is not accessing the internet, and pings to the router result in <1ms.
As soon as I start doing something with the PS3, the pings jump anywhere from 100-1000ms.
When I access the router menu and ping a specific website, all is well. But for the PCs and PS3 accessing the network wirelessly, it's all screwed up.
I'm going to play around with the settings, and I'll let you know if I find anything that works. In the mean time, I have an old WRT54G that I'm going to configure as a bridge until I have the time to troubleshoot this problem.