How to keep multiple connections to internet?

Solution 1:

On windows, ForceBindIP allows you to link specific applications to specific network interfaces. E.g. you could set up internet explorer to connect through one and firefox to connect through the other. The network interfaces are identified by their IP address, which you can discover by running ipconfig on the command line. I haven't tested it.

An alternative solution which requires less command-line-fu is to run a virtual machine. VM software typically allows you to chose which network adapter is used by the VM. This doesn't have to cost anything; you could use the free vmware player with a free browser appliance (i.e. a preconfigured VM with ubuntu+firefox). The network bridging can be configured with c:\program files\vmware\vmware player\vmnetcfg.exe, which needs to be run with admin privileges.

edit: this answer shows how to configure a preferred network adapter on the physical machine.

Solution 2:

You can also use the ROUTE command in Windows to change the metrics of the adapters. A lower metric means that adapter/route is preferred. You could set up some scripts that would change the routes from one adapter to the other.