The .dat extension is a very generic one. What format is the file? If it's
strictly a text file, you'll find that if you try to link to it, Access is
going to treat it as read-only. See http://support.microsoft.com/?id=306144
(and the page to which it links, http://support.microsoft.com/?id=245407 )
for details about this (while the articles talk about importing, it applies
to linking as well)
