No worries, are you migrating to a new 2003 site / org name etc etc ? if not then why not try an inplace upgrade ? ok i wouldnt even attempt that with 2k but i tried it wwith a spare old NT4 BDC and it worked a treat after 2k cocked it right up.
the exchange part really is a doddle mate, i wouldnt try to upgrade but to add a new 2003 exchange box into each office if funds permit (likely as 2003 will need more memory and cpu grunt - but much smoother than 2k)
and simply move mailbox as you would with 5.5 to another 5.5 box
One thing - you can use the other exchange migration tools (export to PST and import in to new mailbox) but they often leave the users not able to reply to mail from an external source as it will go back as undeliverable and a few other quirks
Aelita is a bit tough and daunting to begin with, but it really does work and is a no loss fully roll back bit of software. I picked my 500 odd off in batches of 10 or so, then got them to reboot to be safe, only about 3 profiles got mullered in about 500, and this was down to NT4 OS and a old PC's
Fred, if you want to talk to discuss or need any help or have any questions then feel free to PM me for my numbers mate
I wasnt really looking forward to doing all mine and it did take about 3 months to complete, but looking back i worried for nothing and really enjoyed it and learnt loads, but you are doing the right thing by practising first and getting used to the interface of exch 2003.
You are more than welcome to come visit my workplace and see all my systems and how they are setup and working to get you into the feel of things
Or you can give me a job in yourplace and have someone who has done it before to help out !!
