You can install a local copy of libxml2 as a non-root user, according to this entry in the libxml2 FAQ - that should get around the 'system packages' requirement. Alternatively, the xsdvalid tool from XMLmind looks like it might be a less involved install than libxml2.

If installing anything non-Perl is out of the question, you could, if you're desperate enough, use the online XSD validator. Which is currently displaying:

Operational Troubleshooting in Progress

The Gotdotnet team is aware of the current site operational issues and is working on a solution. Thanks for your patience.

But, hey, it's free... ;-)