The KB http://support.microsoft.com/kb/942866/en-us  discussing the behaviour of maintenance mode when you need to completely take a computer offline in OpsMgr07/Essentials is now available.

 

See AgentMM (http://blogs.technet.com/cliveeastwood/archive/2007/09/18/agentmm-a-command-line-tool-to-place-opsmgr-agents-into-maintenance-mode.aspx) or the PowerShell script (http://blogs.msdn.com/boris_yanushpolsky/archive/2007/08/06/so-what-is-in-maintenance-mode.aspx) as easier workarounds.