I am using the Windows Wireless Connection Manager. On a couple of occasions I've seen that particular AP (don't know what firmware) suddenly stop attempting to authnenticate clients (it never sends any RADIUS requests) and power-cycling the AP "fixes" the issue.
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.
Recently there has been a lot of attention given to the Remote Desktop Protocol for attacker.
The protocol has seen a work in 2011 that abused week passwords and it’s features to copy files and infect other machines and now in 2012 there is a remote code execution bug in the protocol it self.
WPA2 is supported as i can connect to WPA2 personal APs. During the connection it flashes that it "connected" for a second then goes to "Validating Identity" which it eventually timesout on.
For detailed information about how to deploy a wireless LAN using IEEE 802.1X authentication, see Deployment of Protected 802.11 Networks Using Microsoft Windows.
For information about how to troubleshoot wireless connectivity on wireless networks that do not use 802.1X authentication, see Troubleshooting Microsoft Windows XP-based Wireless Networks in the Small Office or Home Office.
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).
I'd start by reviewing the event logs on your IAS server for reasoning as to why it's not authenticating your client.