I just got a TP-Link TD-8616 modem up and running but can't seem to get the Linksys WRT54G running. I have a static IP that Sonic provided and plugged it into the TCP/IPv4 properties on my computer to get the modem working. I also inputted the static IP into the router's settings and disabled DCHP server. I tried changing the IP's of both the router and modem. The modem is in Bridge LLC encapsulation mode.
I'd peel that onion in layers. Set sonic to dynamic, set the TP-Link TD-8616 to be your router. Get it all working. Then flip to bridge mode. Then introduce the static IP.
The Sonic static IP does NOT belong in your TCP/IPv4 properties. The TP-Link TD-8616 should be transparent. The WRT54G should talk to sonic via static IP. Your computer should talk to the WRT54G via DHCP, unaware what's going on behind the scenes.