How does Win 7 handle internet connection when on multiple networks?

I have a computer which is connected to 2 networks which have internet access and a different public IP. (Different ISPs as well). One is connected via an Ethernet cable and the other via a Wi-fi adapter.

My question is, how does Windows 7 handle internet access when connected to multiple networks with internet access? Does it prioritize one and not use the internet from the other, or does it use both randomly at times?

Also, can I change that behavior so it uses the internet from only 1 of those networks and not the other one's?

Thanks

A question that could be asked is whether the 2 [or more] Networks need to be kept separate?

There is a Bridge feature for connecting the same computer to 2 Networks but I can't answer as to the Internet question as the one time I've seen it working only one Network had the Internet service.

A few links that may come in handy:

networking - Two network connections are available to Windows 7 -- which will it use? - Super User
networking - Can I route programs to two internet connections simultaneously in Windows 7? - Super User