Unzip the geopress folder in the zip file to your wordpress plugins directory (wp-content/plugins).
Activate the plugin from your admin panel.
Register and add your Google or Yahoo Keys in the Options panel
Optionally, add http://mapufacture.com/ping/api to your "Update Services" under "Options" -> "Writing"tion which pops up a map and lets you search for the point you want to display. (Itís cool, try it out)