I get "System error 67 has occurred. The network name cannot be found" when trying to map a drive with this command:

net use G: "http://teamserver/sites/teamsite/teamlibrary"

The odd thing is that I am successfully able to map a drive letter to another instance of Sharepoint on the same server, for example:

net use F: "http://teamserver2/sites/teamsite/teamlibrary"
(successfully maps drive F: )

teamserver and teamserver2 are two instances of SharepointPortal Server accessed by host headers by clients.