Windows 7 - Internet connection priority

I've got two internet connections: cable (1) and 3G modem (2). I need (1) to be the default one, and for the (2) to be used only when (1) is down. I've tried to change the metrics value in the connection preferences: "1" for (1) and "9999" for (2).

Unfortunately, this value is not saved, a message says that the connection is in use right now and that the changes will be applied after the reconnection. When I reconnect, metrics value switches back to "automatic".

The IP address for (2) is dynamic, so I have no idea how to use "route" for these purposes (actually I don't know how to use it at all).

Now (2) is used as a default internet connection, and (1) as a backup. I want it to be the other way round.

Would appreciate any help.

Thanks in advance