Sure. You can execute the command 'ipconfig' and parse the output with the script. Another more kludgy way is if you do NOT have dial-on-demand set, you can ping a known address periodically and check the result.
But allow me to ask an exploratory question: Are you trying to determine if the link is down before you go off to a site, or are you attempting something else? Because it's Windows, there might be a better way to do it. If you can clarify what you're trying to do, we might be able to come with a more 'creative' solution.
Comment on (jcwren) Re: Detecting dial-up connections
I'm trying to determine if the link is up and running before I try and retrieve something. The idea is that the script spends most of its time asleep and wakes up every x minutes. If it can see a connection it goes and gets something (actually some weather data from a local airport) otherwise it sleeps again.