Well, there are a number of GIS packages available. I've been writing some notes on using QuantumGIS http://www.cartographersguild.com/sh...-for-using-GIS It's been on hold while I compete in the current guild Challenge though.

After that, you might want to use a vector graphics editor rather than a raster one like The GIMP to do any final graphics work. Inkscape is a good choice.