If you are using Active Directory, you can query it. It will have the OS and SP
level of any machines that are joined and actively talking to it. Note that it
will not report hotfixes, for that you have to query the machines directly.
operatingSystem: Windows Server 2003
dn:CN=2K3UTL01,CN=Computers,DC=joe,DC=com
operatingSystem: Windows Server 2003
dn:CN=2K3WEB01,CN=Computers,DC=joe,DC=com
operatingSystem: Windows Server 2003
dn:CN=fastmofo,CN=Computers,DC=joe,DC=com
operatingSystem: Windows XP Professional
operatingSystemServicePack: Service Pack 1