There are two basic categories of GPS maps:
1. Vector based. The map contains objects which are made from lines connecting sets of coordinates. There are 3 types of map objects - polylines (like roads or contour lines), polygons (like lakes or parks) and points (like towns and points of interest). To create this kind of map, someone needs to actually trace the desired features and create a list of coordinates to be connected by the GPS software. All of the "classic" Garmin maps are vector based, and most Garmin GPS'es (including yours) can only use this type of map. Most of the maps on this site are vector-based.
2. Raster based. The map is actually a picture which can either be scanned from a paper map or an aerial photo that has been adjusted to be geographically correct. The example you have shown is a raster based map created by scanning a USGS topo. The only Garmin units which can directly support this type of map are the Colorado, Oregon and Dakota series. Your Nuvi cannot use this type of map. The Lowrance Endura, Magellan Triton, and DeLorme PN series all support both raster and vector maps.
So you are pretty much out of luck if you want to use this kind of mapping unless you purchase a unit which supports it. Depending on what you buy, you may need to make the maps yourself as well (such as the "Garmin Custom Map" link that I posted above). The map data itself is readily available for free from a variety of sources, but it needs (1) to be converted to the correct proprietary format and (2) a GPS unit capable of using raster based maps.