I believe there is a problem with Windows and the Atheros wireless card. I had trouble getting wireless working when running Windows on my Mac. There's a fix from Microsoft which solved it for me, but I've not been able to find it (yet).
Edit: OK: what wireless security are you using? The problem on my Mac was that Windows has trouble using WPA2 on that (maybe different, but definitely Atheros) card. When moving to WPA it managed to connect. Alternatively, apply the update from here:
http://support.microsoft.com/kb/917021
You might want to try changing the wireless security setting first, to see if that solves it.