I have a Samsung NC-10 netbook which I take to work every day. Most of the time I use it just on the train/bus, but I also use it at work and home.

It has a built-in 3G card which I want to use when travelling, but I'd prefer to use wifi when I'm at work or home, for obvious reasons. Unfortunately, if the 3G connection is up, Windows appears to use that in preference to wifi.

Starting up and shutting down the 3G modem is a bit of a pain - it's not hard as such, just a bit inconvenient. Ideally I'd like it to always be up, and even have the connection itself up all the time, but without routing traffic through it if there's a wifi connection up. This is what my Android phone does, for example.

Is there somewhere in Windows which lets me express an ordering for network interfaces? I suspect the routing table may be relevant, but it's a bit of a pain to mess around with. I'd really expect there to be a simple GUI way of setting this up - after all, it would equally be useful when dealing with wired vs wifi connections.

I'm currently using Windows XP Home, but Windows 7 answers would also be useful as I'll be migrating soon.