DBX files are not autocad files.  They are a database file designed by a
person who now permanently resides in a rubber room somewhere with expert
psychiatric help around the clock [at least we hope he does  ;-)  ].  The
database is designed to take all messages, chop them into 512 byte pieces
and scatter them at random throughout the file.  If you were to open the
file using Notepad (and it's not recommended since changing even one byte of
the file can make the entire file unreadable by Outlook Express) you would
soon notice that it makes no sense to anyone trying to read it.  The design
was apparently considered a "security" feature to prevent anyone from
accessing your stored messages within the file.

One big problem comes with the widespread use of antivirus programs set to
scan incoming email.  Some programs quarantine supect information, while
others damage the file by substituting zeros for the intended bytes, and
again, this makes the entire file unreadable in Outlook Express.  It's hoped
that the next version of Windows (over two years or longer away, since it's
not even in beta yet and presently called Longhorn) will have a completely
new structure for stored messages and will not use any type of database that
is so fragile as the exitisting dbx file structure is.  But, maybe that's
too much to hope for since those users who will not (for economic or
whatever other reason) upgrade will still be stuck with the old system so
we'll be living with the problem for some years to come.  For more info
about Outlook Express in general, along with many problem solving tips and
techniques, see this link:  http://insideoe.tomsterdam.com/

And to answer your last question, for the reasons above, you should *not*
try to open a dbx file.  Let Outlook Express do it and hopefully all will
stay right with your stored messages.  Using any external program to open
them may well damage them.