You must specify the type of file when you want to import it. ACCESS will
not import a .dat file unless you either rename the file (to give it a .txt
extension) or you modify the registry settings.
ACCESS no longer allows importing text files with a .dat extension (security
reasons). Easiest fix is to manually change the extension to .txt (or add
..txt to the end of the filename), and then import the file with the .txt
extension. This renaming (and importing) also can be done programmatically
with VBA code. This article
http://support.microsoft.com/?id=306144 includes
code that automatically makes a copy of the textfile with a .txt extension
and imports that.
Otherwise, you'll need to change the registry settings to allow this import
See
http://support.microsoft.com/default.aspx?scid=kb;en-us;304206 for
information about all of these workarounds.