eval { require DBI };
if ($@) {
   warn "DBI not here.. will keep checking...";
}
eval { require Win32::ODBC };
if ($@) {
    warn "Oh oh";
}
... etc...

##</code><code>##

my %subs = ('DBI' => \&use_dbi,
            'Win32::ODBC' => \&use_odbc,
            'Win32::OLE' => \&use_ole
            );
my @mods = ('DBI', 'Win32::ODBC', 'Win32::OLE');
for (@mods) {
    eval { require $_ };
    if ($@) {
       warn "No $_ here";
    }else{
       $subs{$_}->();
       last;
    }
}