Hmm, depending on how you have your router configured, it may not be auto-assigning dns and ip addresses properly. Are you using DHCP or manually setting them? When you've got a 2in1, usually the addressing is all done for you, but when you've got two separate units, you've gotta tell them to work together - and if it's not done properly, then your ps3 won't talk to the modem. The way you've got it, you've gotta worry about a) your connection to the router (wireless), and then b) your connection to the modem through the router.
My ez-mode suggestion would be to take your router back and try and swap it for a modem/router in one combo, that will make life easier.
If that's not an option, then maybe start by running a constant ping from your pc to your router, and seeing if you can see if it spikes or lags out.. and maybe try and ping your ps3 and see what the response times are like.
Also, I believe a couple of ISP's were having DNS issues last night between 6 and 11, dont know if that was related.
25/07/2008
In front of my PS3