Hello all,
As I have already said so to one of my client, the fact that the Settings tab & Calendar menu are disappearing from the CRM Web Access when Microsoft Outlook is running (with the CRM module installed) is 'by design'!
Of course, this is not quite obvious for everyone! And I don't see why it has been made like this 
Anyway, I've always used the SiteMap 'hack' to display the Settings tab when Outlook is running (remove the Client=”Web” setting for the Settings area in the SiteMap.xml file) but now, I've found an interesting post on the Microsoft Dynamics CRM Team blog that deals with this 'problem'.
You can find it here: Link
Happy 'hacking' 
Mister O.