Hey Doug,
If you are thinking about the Abacus FSRepaint software, then take heed. It is a fine tool for seeing your work "in-sim" without all that reloading effort. I really do recommend it for beginners. BUT you need a paint program for the nut's and bolts.
I've been using the Corel Draw suite since the very early 90's, so I am biased. I bought an "old" version and through that I got the upgrade to the latest at a price I couldn't refuse. PS elements and various others are indeed up to the job of repainting. You can even achieve good results with windows paint ('scuse if I chunder
) you really can - if you don't mind pixel for pixel painting.
Phot-retouching paint programs are the commonest in use these days. Photoshop Elements is very commonplace. Paintshop pro (that's the Corel equivalent) is also useful.
What you will need most is a painter program that allows layers and/or layerable objects. Most modern free-with-a-camera-or-printer painter and editors do the job in a simple, but effective way. If you don't want to spend thousands on full commercial packs (Photoshop CS5 or Corel Draw suite X5[mine by the way]) then I would recommend GIMP - it's basically a free Photoshop clone. Does everything Photoshop does. But as with all open source progs, you have to rely on the community for help. There's a pretty good pdf manual though.
What's missing in Photoshop, GIMP and other similart photo editing programs is a Vector Graphics drawing tool - in the Corel Suite it is actually called Draw (the photo tool is really Corel Photopaint). Adobe produce "Illustrator" for the photoshop painter, but you pay extra.
For first timers, I'd say GIMP. Google it, you will not miss. Steep learning curve if you are starting from scratch with no art knowledge - but not impossible. Fun? Yes! Even with 15 years playing around with computer graphics, my first FS repaint was a disaster. Kitch all the way.
The main things which make painting planes (and other game objects) so challenging is the need to know how the graphics engine interprets your work. Specular, bumpmap, UVs and diffuse maps each have their own secrets you need to be aware of. FSX allows us one helluva lot of possibilities, but there are just so may ways to recreate what you can see in your mind's eye.
Much also depends upon how the model maker has created his model. If the maker has decreed all his surfaces to be polished metal in the export phase of his creation, then there is no way you, the painter, will get a matt finish. And that's just the start.
If a model maker insists on putting as few sheets as possible into the texture file, then you are going to hit "scale problems". The default and the Arosoft Beaver both suffer for instance. I won't even go into detail of how position on the texture sheet affects bumpmap lighting...
Oh shoot! I wrote too much and put you off. Believe me, I don't want to. This whole painting lark is a barrel load of f with a capital FUN
short answer:
GIMP. Read the manual and go to
www.simmerspaintshop.com for the best teachers and help. So what if they paint mostly military. There's tons of tutorials and guides.