I am impressed how easy it is to install the opensource edition
Is there a how-to to upgrade my existing open source edition to the starter edition ?

Can I just keep my existing mailboxes ?
Or is it just a 'add your license key here'.

I am particularly interested in the outlook connector. I've even seen it working under 2007, can you confirm that (latest version 5.0.11) ?

Oh yes, I am using Debian 4.0
Is there a recommendation for VM system in terms of CPU/memory ?