I agree with chromatic's post.

Check out CGI.pm and also
Check out Ovid's CGI Course

Lot's of great info there. I've not read that book either, but I'd use CGI.pm for getting values from web forms, it only takes a couple of lines of code.

To answer your question though, it usually doesn't matter if you call it *.pl or *.cgi. Try both to see if the script works on your web server, if so then use whatever you're comfortanble with.

Good Luck