Maybe by adding a second call to retrieve .htm files?

use File::Find::Rule;
my @files = File::Find::Rule->file()
                            ->name( '*.xml' )
                            ->in( "." );
     
foreach $fname (@files)
{
    print $fname;
}

@files = File::Find::Rule->file()
                         ->name( '*.htm' )
                         ->in( "." );
     
foreach $fname (@files)
{
    print $fname;
}
[download]

Honestly, you seem to be asking quite basic questions that resemble quite a lot some homework questions or questions a corrector would ask of you if you copied some code from your coeds. That's also why I'm giving you a quite suboptimal solution. You can find a much better solution by reading the documentation of File::Find::Rule.

RTFM

use File::Find::Rule;

my @files = File::Find::Rule->file()
                            ->or( File::Find::Rule->name( '*.xml' )
                                                  ->name( '*.htm' ) )
                            ->in( "." );
     
foreach $fname (@files)
{
   print $fname;
}
[download]

Ug, let's make that less horizontal:

use File::Find::Rule;

sub FFR () { 'File::Find::Rule' }

my @files = FFR->file()
               ->or( FFR->name( '*.xml' )
                        ->name( '*.htm' ) )
               ->in( "." );
     
foreach $fname (@files)
{
   print $fname;
}
[download]

You probably don't need or for name since you can do ->name( '*.xml', '*.htm' ) and ->name( '*.{xml,htm}' ), but I included this as an example in case you needed to join other rules.

Continuing with what Corion said (read the documentation), if you have a module installed on your system, you can access its documentation by using perldoc from your command line. For instance, to read the docs on File::Find::Rule, you would type:

perldoc File::Find::Rule

Also, to learn how to use perldoc you can type perldoc perldoc and to get a listing of all of the documentation for perl (not modules you may have on your system), type perldoc perl