Plantronics Headset with 13" Bootcamp

Heya folks, did a bit of searching on the forums, and couldn't find any clear answer to this problem, so I figured I might post and see if any of the more expert people can figure this out.

I've recently started using Skype a lot more than I used to, and so I decided to buy a proper headset. Got a nice little Plantronics one, seems like a good unit. So I plug it in, one plug into the headphone jack, the other into the mic jack. I can hear without a problem, but Windows is still using the internal microphone.

Is this just a matter of fiddling with the settings, and if so, which ones? Or is this a hardware compatibility issue, and if so, what would work hardware wise?

MacBook 13" Late '08 running Windows XP SP3.

Mhmm, I've tried playing with every sound option I could find, Windows can't seem to detect anything other than the built in mic. I've been reading through some other forums, and some folks say it might have something to do with the MacBook's using a line-in instead of a mic-in. Can anyone confirm if this would be an issue?