Sounds like your mod_perl was built with Perl 5.5.3. If I were you, I'd not muck with @INC in this case. Instead, I'd do something like this:

BEGIN
{
    require '/path/to/DB_File.pm';
}
[download]

No guarantees -- your system sounds somewhat screwy, but I'd use that as my next try.

Update: corrected minor text typo