You may have to enable 802.1X authentication on your Windows Vista machine.
To enable 802.1X Auth:
1. Open Manage Wireless Networks by clicking the Start button , clicking Control Panel, clicking Network and Internet, clicking Network and Sharing Center, and then, in the left pane, clicking Manage wireless networks.
2. Right-click the network that you want to enable 802.1X authentication for, and then click Properties.
3. Click the Security tab, and then, in the Security Type list, click 802.1X.
4. In the Encryption Type list, click the encryption type you want to use.
On wireless networks, 802.1X can be used with Wired Equivalent Privacy (WEP) or Wi-Fi Protected Access (WPA) encryption.
5. In the Choose a network authentication method list, click the method you want to use.
To configure additional settings, click Settings.
It could be that the option selected in step #5 above is incorrect. It is probably trying to pass the local username and password without prompting you.
I hope this helps. If so, please rate.
