I've downloaded HTML::Parser and HTML::Tree as a start

Given that I really hate to assume about anything, but do you mean you ftp'ed the tar files and unpacked them somewhere or did you invoke

perl -MCPAN -e 'install HTML::Parser'
perl -MCPAN -e 'install HTML::Tree'
[download]

If you did the former you should have done the latter to install the modules appropriately.

Hope this helps.