If you mean street maps supplied by third parties, Howard2K's suggestion of Pocket Streets might work for you. Other solutions include Mapopolis, Routis, and a couple of others whose names I've forgotten - check in the GPS forum for details.
If you mean you want to create your own maps, or save Mapquest (or the like) maps as graphics, then you could use Sunnysoft's
MapView which allows you to define a set of graphics as sections of a larger scrolling map. You can drag the map around to view it, mark points of interest and name them, and use it with a GPS unit.
MapView isn't free but it's very inexpensive. There might be free programs that do the same, but if so I haven't come across them.