There are generally only 5 reasons a Windows 2000 or XP machine will not respond to a WMI Inquery: Firewall, Impersonation level, Remote DCOM, sharing security, or account authority.

The Windows XP (SP2) Firewall can prevent the computer from even being pinged, as well as replying to WMI requests. Selecting this option will disable the firewall.

Impersonation level determines what credentials get used for inqueries. The setting '3' (impersonnate) is the recommended setting.

Remote DCOM is normally enabled. If it is disabled, the queries will fail.

Sharing security only applies if the guest account is disabled. If the guest account is disabled, Sharing security must be set to classic.

You must have the rights on the local machine to perform a WMI scan. If the machine is not a member of a domain, you can create a local admin account and run the scan as that user.