SMS 2003 - Tools - Active Directory Janitor
When dealing with Active Directory machine accounts within SMS 2003, you will eventually have to deal with accounts which continually turn up as non-clients. In many cases, this is due to the machine not actually being valid any longer, but still being listed within Active Directory. AD System Discovery will still pick up the account and attempt to resolve it and, not being able to, will throw it into the non-client collection (if you have one.)
I have found it beneficial to periodically go through the non-client collection and run AD Janitor against the exported list to get statistics on those accounts. With this utility, an administrator can determine whether the account can be deleted by reviewing the scan report. So, if your Active Directory is "less than clean," pick up this tool and make your coverage numbers look better.
http://www.specopssoft.com/products/adjanitor/