To start, here is my current setup:
The dotted lines are a wireless connection, solid line is a wired connection.
I originally was just connected to my home network via network 1. Unfortunately, I lost my wireless adapter for my 360. So I hooked up my 360 to my PC with an old router so I could still stream videos (router 1 is too far from the 360 for a wired connection).
Both networks work individually. But when both are enabled on my PC, I can't connect to the internet. I have to disable my connection to the second network in order to be able to get on the internet. I'm not sure about connecting to local PCs, haven't tried it yet. When both connections are enabled though, I can still stream to my 360 properly.
I'm guessing the problem has something to do with the computer not knowing which connection to use for internet, but I can't figure out how to set that.
By the way, I'm on Vista x64 Ultimate SP1.
+rep to whoever can fix this, disabling/enabling the connection all the time is annoying.