The Contact Form (actually all of our solution packs) are not extensions so there is no mxp and you do not need the Extension Manager. It is a pre-built form. Here is the Getting Started Guide for this solution:
contact_form_sp_gsg.pdf
If you are having problems with a certain step in the guide, just let us know and Tech Support will help you through it.
Other how-tos, etc. for the Contact Form:
contact-form/