"Seeing" both ways across router?

I'll assume the wired clients are plugged into the ethernet ports on the WGR614v5 router.
I'll assume Windoze XP SP2 Home on all the clients. Did you disable or create an exception to the Windoze firewall? That will prevent any incoming network connections but allow outgoing. Control Panel -> Windoze Firewall -> Exceptions Check the "File and Print Sharing" box. If you're using a 3rd party software firewall such as Norton, McAfee, Zone Alarm, Kerio, etc, kindly disable it temporarily to see if that fixes the problem. Norton Firewall 2005 is expecially difficult to configure.
First, see if you can ping each client from the other. Nothing is going to happen until everyone can ping everyone else.
I like to use: Windoze networking help. It's kinda rough finding the appropriate articles, but worth the effort as they are rather easy to follow.
I should hope not. Your SpeedStream 5100(b??) is acting as a modem. Actually, it's an ATM to ethernet bridge, but that's not really important for this discussion. The WGR614v5 is a router. The ethernet and wireless ports on the LAN side use bridging to connect. I think this is what you mean by "configured as a bridge". It is possible to configure the WGR614v5 as an access point (bridge) by ignoring the WAN connection on the WGR614v5. Is this what you're doing? Is the speedstream modem plugged into the WAN (internet) port on the WGR614v5 or into one of the LAN ports?