I have an Exchange 2003 box that is seriously overstressed.
I want to transfer its duties to a new and faster box.

I don't cannot suffer downtime, so I have to do this stuff live.

Here's what I plan to do:

• Install Exchange 2003 on the new server
• Set up the new server, so it will accept requests from users for their mailboxes
• I want to do as little manual set up as possible, because that 'll eat up my time and is too error prone
• Than I want to transfer my datastores one by one to the new server and have those users (once the datastore in the new server is up and running) to get their data from the new server (without them noticing)
• I don't have to transfer all the datastores, some of them need to stay on the old box (because I'm still waiting for extra HD space to arrive from the supplier)

What steps do I need to follow to do this?
The new box has never seen this domain before, the old exchange server is not the DC, we have a dedicated DC.