First, LOVE Gravity Forms - totally awesome tool!!
The conditional logic is great, i.e. only show fields that matter for the topic of the contact - so a person contacting you to advertise will see different fields than someone contacting you with a support question.
However including this in the form description won't work, since the entire form is hidden.
You could put the above code in the WordPress page itself (HTML mode), but the WYSIWYG editor mangles it every time when switching between HTML and Visual view.
Here's the dev site page I'm testing this on - http://blogsuccessjournal.djmdev.com/contact/
if there's not a way currently to show a block of HTML above the form, that could be a great additional field under form settings. :-)