My take is that Macs strive for a reliable connection and having a Linksys and a D link in series is going to give you drama unless you know how to fiddle with all the settings, and it probably will never work with iChat audio/video. Second issue is our Telecom gave out those D Links out like candy - any time you complained they gave u another one. A number of bods i have helped have had no troubles after we ditched the 502 - so that may be a good starting point.
Does the Linksys not have a modem?