I've exported them to a .csv file before with Exch 5.5. You need to add all of the columns you want to export to the custom recipient view in the Exchange Administrator program, and then choose the File -> Save Window Contents command.
This is, quite honestly, an ugly way to do it , but it's the only way I've found to export the custom recp. data. I've never re-imported back into the Administrator program - typically I suck the data into an Outlook Contacts list or public folder, but since it is in .csv format you should be able to get it back in without much grief.
Good luck -
Chad Stiller, MCSE
Ramcom Technology
cds@ramcom.com