Date: 5/7/2008 1:13 pm EDT
If by "hardboard" you are referring to a product such as "tempered-masonite" then that product wouldn't be the wisest choice. A plywood underlayment would be a much easier material to work with. Screws also wouldn't be required and would be a waste of money and time and problematic to install and would offer no gain. Typically 1/4" crown staples are used for this type of installation. Nails can also work.
More importantly is that your substrate is "plane" to within 1/4" over 10 feet of distance.