I just took an interest in html embedded perl and started reading this:
Embedding Perl in HTML with Mason
which is free online and you should at least be aware of it.
For sure: do some CGI stuff. You actually do not need to use *any* perl modules at all to do CGI (which is not to say they are not useful). Using the basic "CGI" one will spare you some simple parsing tasks also probably covered by PHP, and provide you with some helper functions as hinted at behind Corion's "curtain" -- but it is not (just to let you know) strictly necessary. CGI just works via <STDIN> and <STDOUT>.
If you want to get your basic perl skills up to snuff I'd very strongly recommend "Intermediate Perl" (Schwartz, foy, Phoenix).