Check out a software package called expertgps at expertgps.com. It is very inexpensive, and uses the same USGS topos, and also aerial photos, that the more expensive programs use. Once you view an area while at home on your laptop, it saves the image files, and you can then go to the field, and show your position in real time on both the aerial and topo maps. You can create waypoints, tracks, routes, and upload or download to/from the GPS, and do a zillion other things with it. It was created by a genius name of Dan Foster, and any future upgrades are free to current users. I use it a great deal in both my forestry work, and for hunting. I'd hate to go to a new area without it!