Resource in Use

This is for reference:
If the datastore displays "resource in use" when trying to delete it.
Go to one of the command lines of the Clustered vSphere ESX servers and type
vmware-cmd -l ( that is L as in Larry)

This displays the attached vm's to the host and detaches the datastore from the hosts.  The remainder rescan and detach once you delete it from the single host.

ESX vSphere 4.0 u2