Couple of options:
I've done this in the past:
1) ghost the partitions to a file server using a dos ghost disk (I can help on this if you like), then boot the new machine and put the image down on it. Norton ghost will let you put different partition sizes together, so say you have a 2GB boot partition, and a 7GB data partition...setup your new server with the partitions you want, say: 4GB boot, and 14GB data, and then you can ghost the small partitions to the new server and still have the extra space.
2) setup your new machine, install software, etc. I believe the Exchange 5.5 files are simply the .edb files in the exchange server directory. I was told that if you simply copy these files to the new server, restart the services, and you should be up and running. I've never tried this technique, but it's worth a shot!