Just connecting your laptop and the PhotoBridge together with an ethernet cable won't work, as na9d mentions you'd need a different type of ethernet cable - a crossover cable.

Are you sure when you tested the ethernet bridge with the laptop that you were testing it and not some built-in wifi functionality that a lot (most) of laptops have nowadays?

Unfortunately, not being able to see shares means (as you suggested) one of three things (as it now has an IP address)

1) The ethernet port on the PhotoBridge doesn't work correctly (check the lights on the back of the PhotoBridge)
2) The ethernet bridge is not working (poor signal strength or not configured correctly)
3) It is working, but you have some sort of problem seeing the shares (say because you have a firewall, or you're using a share name with spaces).

The only way I can think to solve this is to bring the PhotoBridge to the router, either long cable or physically move it. Then get it working there (removing possibility 1). Then see if you can find shares. If you can, then back to trying the ethernet bridge.
Sorry I can't think of an easier way.

soiaf is correct. The best way to make sure that you can get things working is to go wired. Get things working that way. Then once it is up and running, introduce wireless to the mix. But as I say, Wireless can be problematic.

It may be better to get a Wireless USB adapter and plug that into the USB port on the PB rather than using a bridge. This way, you'll be able to use the PB's built in Wireless functionality and you won't decrease your available wireless speeds due to the bridge. Check which adapters are compatible on the Roku website.

As an example of how much better wired is - Roku has several art packs that can be run from a shared file space. One is the 3 minute long aquarium module. The documentation makes clear that a 100 Mb/sec WIRED network connection is needed.