These tips are based on my experiences and not official documentation.
C:\Documents and Settings\*Windows User Name*\My Documents\Palm OS Desktop\*5 char of your Palm User Name*\datebook
for me it was: C:\Documents and Settings\Nate\My Documents\Palm OS Desktop\GoodMa\datebook
Close Palm Desktop if it's not already closed.
Find datebook.mdb and Rename it to datebook.mdb.lost
Now find the most recent backup file (.bak). This BAK is the MBD file from a previous session of Palm Desktop. Probably "DateBook.bak" Rename it to Datebook.mdb
Palm Desktop should make a new DateBook.bak file at some point after starting the application.