I haven't used ActivePerl for at least a few years, so I'm not familiar with what modules are available via ActiveState's repositories.
If you're using 32-bit ActivePerl and still have access to ActiveState's repository for your version of ActivePerl (i.e. using the latest build of the community version or have purchased support for an older build), you can use PPM to install MinGW and dmake from their repository. After installing both of those, you can then install modules directly from cpan. In this case, the command to run is 'cpan install HTML::Valid'.
Alternatively, you can also try using Strawberry Perl, which comes with everything needed to install modules directly from CPAN. Also, Strawberry Perl offers a portable version that does not need to be "installed". Just download and extract the zip file and run the portableshell.bat batch script.