Software

I don't think it is recommended to run exchange 5.5 on server 2000.

I also don't think you can just copy the info store to a new computer. MS has a reference article on how to move an exchange 5.5 server to new hardware.

(involves, installing exchange 5.5 with the /r option, copying the database files, removing the old server from the domain, having the new server join the domain with the same hostname and IP, applying the Service Packs...)

I did this a long time ago. After I had Exchange setup on the new server I moved the mailboxes, some in groups, some individually. You will also have to move the Public Folders. Leave the old server up for a few days so everyone has a chance to log in and update their Outlook. The take her down a wait for problems. Ususally the worst problem was redirecting Outlook to the new server. There was no down time except when I changed the IP address to accomodate the external mail.

This same thing was done at our office a couple years ago. Also, we are a smaller company so this wasn't that big of a deal but this wouldn't work too well in a larger organization. The administrator at the time set up new mailboxes on the w2k server for everyone and used Exmerge 2000 to merge all the mail to the new server in the user's new mailboxes and then switched Outlook over their new mailboxes. It was moreless a weekend job. This way you're at least avoiding any potential problems with moving the database files and such. Just a thought.