I like to stream content to my xbox. I have two internet connections on two different networks. How would I go about being able to share from both networks to my xbox without giving up any net bandwidth between them? Is there a way to do this?
A few ways, one is to get a multiple-uplink router (Linksys has a couple VPN routers with dual WAN ports), another is to build your own *nix router that has support for load balancing. I don't know if the Linksys hardware supports load balancing, but I think it does.
Any router with multiple interfaces should work although for home use (cheap) a linux box should work fine. You just need a route from one network to another. Your default gateway will still be whatever cable routing device you use, but if you want to access the other network it will fire you off to the appropriate interface. This router will sit in between the two devices that you are using for your internet routing.
Edit: that linksys should do what you want for less money than another computer, but it looks like some people had issues with it. If you have ANY old system laying around, throw a second NIC in it (if you don't have two nics on it already) and fire up yoru favorite linux distro. There should be plenty of canned router distros out there too, you can probably run it off cd, floppy, or USB key.
What about if you have 2 wireless networks? I'm trying to do exactly the same thing as the OP, and I also have two separate internet connections coming into the same location, but they're at opposite ends of the house on wireless routers. Running a crossover cable from the routers to the switch wouldn't be very feasible.