I would first suggest that you clear out any of your temporary internet files // including history, cookies and cache. If you just added a router into the group, then anything in cache may be a problem.
Then make sure that your router is configured properly, with your isp's primary and secondary DNS information. Make sure your router has a static ip address and that the computer has the gateway pointing to that router ip address.
Depending on which OS your computer is running, I have also found that in W2K and WXP, that it helps speed things up if your also put your ISP DNS information into the computer as well.
You should also make sure that any PPoE adapters are removed from your device manager, because your LinkSys shouldbe handling the PPoE part of DSL. Make sure that that box is checked on the router configuration screen.