Hm. The problem appears to be in the library itself. It's not including its own prefix for the sub-modules. In other words, it's doing:

use NewsML::Node;
use NewsML::IdNode;
use NewsML::AssignmentNode;
# and so on
[download]

instead of

use Syndication::NewsML::Node;
use Syndication::NewsML::IdNode;
use Syndication::NewsML::AssignmentNode;
[download]

Probably the easiest fix is to add a use lib statement at the top of your program, like so:

use lib "C:/Perl/site/lib/Syndication";
use Syndication::NewsML;
[download]

And then it'll find the other modules.

It may be worth filing a bug report via CPAN RT, even though it appears the author hasn't worked on it since 2002.