To fix the issue of internet not working on linksys wireless router or any other router after connecting it to a different adsl model you simply need to release and renew the DHCP.
Click here : If you can’t access linksys wrt54g admin panel
For linksys wrt54g do this to release and renew DHCP:
Login to linksys wireless router admin control panel (usually by 192.168.1.1) in web browser and login
Goto: Status (first sub page will open itself: Router)
At the bottom of the page find 2 buttons: DHCP release and DHCP renew
Click them one by one and wait for a while.
Disconnect the wireless internet from your device and connect again in case renewing don’t fix the problem.