Final resolution: I am posting this in order to help others trying to do the same thing. I was able to create a new NUTD database ONLY in this fashion (I am trying to go from NUTD 3.5 for OS 9 to NUTD 5.3.2 on Leopard):
export a text version of your database in NUTD 3.5
You can try to import that directly into NUTD 5.3.2, but it may not allow you to select the file under import. You can try adding a .txt extension. But you will probably get many errors and fail.
The errors seem to be of 2 primary varieties: "Inconsistent event data" which means you have events that cross 12 midnight, or errors where an expected field is not found. In my case, this was almost always the last 2 fields (server and "done" for those errors, there are tabs missing in the line--make sure there are the proper number of tabs to correct those errors). To fix this, I would recommend using a text editor that allows you to see the tab and return characters. I found Microsoft Word to be good for this--just make sure to set the page size large (I used 22"x22") and type size small (I used 3 points) to see the data all in single lines. You'll need to make the changes manually or by using find and replace (useful, but doesn't always work). resave the data as a text file, and try to use the import feature. IF NUTD will not allow you to select the text file, the only soultion I have found was to install the trial version of NUTD 4.5.2 (uses the NUTD 5 format), and import into that. You will need to select "all files" when you get to the navigation window to select your file for import, as the "text" file filter does not work. If you have no errors, the file should import fine, and you will be able to save a copy. That should open fine in NUTD 5.3.2 on Leopard. If you get an error, note the line number and check that line in your text editor. Good luck! '