Actually there's a stupid cool tool called DD - you can use DD to create full disk images in real-time AND you can transter the images when completed via SSH, FTP, drop 'em on a USB or do pretty much anything you'ed do with any other complexticated software.
DD is already there on your machine too, so you literally just Google for something like "use DD to make disk images" and there's a crazy well written article about how exactly to do it and even how to automagic it so it just works without doing anything else.
It even cleans up after itself!!!!
On a side note did anyone happen to mention you can't import PST's into Zentyal from your SBS??? True fact, it'll make your Zentyal server go down faster than a drunken prom queen if you know what I mean.
There are a TON of IMAP transfer solutions out there, that's what you'll need for mailbox moving and then you've gotta figure out how on Earth to export your calendars as iCal's and your contacts as Vcards. Legit, that's a HUGE pain and I lost a lot of hair on that end of the world!!!
I've been on a crisis recovery mission lately for a TON of places around here so I'm not here all of the time, but if you run into anything else just drop a new post in here and someone will be able to get you.
Good luck!