Like Ovid and Masem, I'm going to recommend an external tool.
If you (or your designers) are using Macromedia Dreamweaver for page design, there is a really nice extension for testing usability on the Macromedia site. It is configurable and is capable of some very detailed tests.
If you decide to go ahead and build something similar in Perl, though, I'd like to see it! :-)

Impossible Robot