First off, I am a novice map maker. I have never before created a map using software of any kind (not counting a rather tragic attempt using MS Paint). At present, I am gathering the tools I will need to build a world map, regional maps, interior blueprints, and city/town maps for a world I have imagined for quite some time. I have a few questions I need to answer before I get started.

I have access to the latest versions of GIMP (2.4.2) and Inkscape (0.45.1). I also have access to TurboCAD (a stunted version of AutoCAD).

I have recently been given an older version of Photoshop (4.0 to be exact). Is it worth my while to use it? Are there features and tools in the later versions that don't exist in 4.0 that are crucial to creating an artistic-style game map? Are there features and tools in 4.0 that I can't find in any other program (other than Photoshop, of course)? Do I need this old version of Photoshop at all?

I have experience with TurboCAD (not much), and part of my job is to create functional blueprints for homes. So I am fairly comfortable with that aspect of my overall goal. However, I don't know much about the capabilities of the other programs, and I don't want to waste time learning software that I am not going to use. Any guidance would be greatly appreciated.