Best said:
Is there a way to access .DBX mail files, on a computer with a Vista OS,
that were backed up on another computer with an XP OS?
This has little to do with the OS, except that DBX files are for outlook
express, which won't work on Vista. You can import them to Windows Mail
etc if you have the key contents of the folder, specifically the file
'folders.dbx'.
If you have that file, you can point the import utility to an OE store
folder, and then import them. If you don't have that file, you can
re-create it with an amount of back and forth with another OE install on an
XP system, then use the folder to import.
HTH
-pk