Is the old exchange server a exch2k server? is the new and old server in the same domain? If this is a replacement machine you could simply use Exchange merge utility in the support tools to export and import.
If all of the user accounts are the same, you might have some luck with just copying the private information store file to the new server and attempting to mount it and copying over the data that way. If that doesn't work, export the old mboxes to PST's and import them into the new exchange installation.
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Move Exchange Data
Thanks for the help.