Here is a video explaining how to do it.
 
YouTube Version:
 
and a Screencast version if YouTube is blocked by your IT dept
Here are the instructions for sharing the Data File between two computers that are not networked...
If you want to  access the data on the memory stick or Zip Drive or Portable  Hard Drive and not actually
copy the data from the Zip Drive  or Portable Hard Drive to the new computer.  
To see an example of USB drives click here  http://tatems.com/tips/USBDrives.cfm
Then in TATEMS you will need to  click on tools-->Networking and point to the data file  on the memory stick or
Zip Drive or Portable Hard Drive then  choose link now.  
If on the other hand you want to actually copy the data  from something like http://dropbox.com or USB memory stick or Zip Drive or Portable
Hard Drive  or CD-R to the other computer then you will need to do  that using the reverse procedure that
you used to copy the data file to http://dropbox.com or memory stick or Zip Drive or Portable Hard Drive or CD-R in the first place.  
You should also store the registration key for both computers in the master data file.
You can do this by opening TATEMS on the computer with the most recent data and enter the
registration key if not already entered. We'll call that computer 1.  Then close TATEMS.
Then copy the data file to the other computer(Computer 2) and open TATEMS on computer 2
and enter the TATEMS registration key for computer 2.
Then copy the file back to computer 1 and then open TATEMS.
At that point the registration key for both computers 1 and 2 is stored in the
data file and you should move forward with that one. ( the one on computer 1)
Remember to keep track of which data file has the most current information
on it and not to overwrite it.
There is no way to synchronize two data files.  
One will always be the master data file to be moved  back and forth between computers.