I suspect a firmware upgrade probably fixes that behaviour. If you want to accept both computer credentials and user credentials you'll need to name both "Domain Comptuers" and "Domain Users" in your policy.
By default, XP will re-authenticate with the user credential after the user logs-on (there is no way to do computer-only with XP, I believe).
The service uses the SSID newcastle-university with Wireless Protected Access (WPA) and Enterprise level encryption (EAP).I cannot get WPA2 enterprise to work on my network. Windows Domain, using IAS and its own CA Linksys WAP200 Access Point I setup the AP to use WPA2-Enterprise Mixed using RADIUS I setup and registered IAS on the domain controller.