is your router a LinkSys?, there's a known issue that hasn't been fixed that the PS3 just fucking hates the LinkSys routers and all round systems, on most games you get lag... on KillZone 2 a game that demands about 65% of your connection it'll kick you out.
http://homecommunity.cisco.com/t5/Wireless-Routers/Playstation-3-problem-DLNA3-WRT54G/m-p/78107
When setting up the connection again, try to have the PS3 hooked up by ethernet or as close as possible to the router to get a better linky thingie whatever.