OK, I started out using Abacus FS Repaint, but I found the built-in editor to be total kludge... and I don't even know jack about image editing.  So I found GIMP and used Abacus to create new variation and open it in GIMP, I've had a blast painting up the default King Air (for FSX), but now I don't really know how to make it back into a .dds file or whatever I need to do to get my new repaint up and flying.
I've got my new paint job saved as both .xcf (GIMP's format) and as .bmp, I think they're in the Abacus folder.

Go and download this Program (Freeware), you'll have to google it.

"DXT Bitmap" file converter

Then you'll be able to convert all kinds of files and work with them and convert them back to whatever.

Don't forget that with DDS files, their usually flipped upside down and Mirrored.

Also,, I use Paint Shop Pro #9 to do most of my Painting and sometimes Texture work.

You can also use Photo Shop if you choose to.

Another Handy Freeware program you need is PAINT.NET 

with Paint.Net, you can also take images and paste them right onto the aircraft, with just a tad bit of editing beforehand,,, as far as the image your wanting to paste, suit it to your liking 1st.

YOU TUBE has some great Painting Help tutorials on painting Flight Sim Aircraft too !

Thats how I learned by watching the video's then trying it on an Aircraft I really didn't care if I messed up or not,,

so try all those programs I listed above, give er' a go, and practice a few times learn the program, itself and what all they can do, and can't do - have paintence , a lot of it,, do just minor changes at 1st to get the hand of it,,, in time you'll get better !! 

Paint.Net

DXT BIT Map file converter

Paint Shop Pro

Photo Shop 
 
http://www.youtube.com/watch?v=TVcGUFPfsF0

Just some Video , but it gives you a general idea, look for other videos too !

Jetranger 

Ugh, it STILL loads as the original plain white aircraft.  What am I missing?

Converted the extended .bmp to .dds DXT 5

So have you got the DXT Bit Map Converter yet ??

I really want you to get that and learn how it works,, it can make manuiplating your files easier for you !

Also, when you get it, sometimes the 32bit 8-888 file can sometimes display the file,  in the BITMAP format,, providing the other files are of BITMAP too !

Tho if you study other download of Aircraft files - you'll sometimes see on occasion both DDS & Bitmap files with the same aircraft, sometimes , not all the time tho.

I studied all kinds of other Aircraft files, to get the hang of it, with that DXT BITMAP Converter you can click on the file and open it to see what texture format it is,,, just to get educated as to how others have set it up and how its used and on what files.

Some are DXT3 or DDS, theres like 11 different types of DDS files to choose from,,, mostly for FSX tho in that format.

but you'll need that DXT Bitmap converter to see all that,,, 

lets us know how your coming,,,

send sum photos !

and remember be paietent,, takes time to learn all that stuff - rome wasn't built over night and neither was a Boeing or Lockheed or Beechcraft !!     

Jetranger

GAHHHHH... GIMP does its own thing when it saves files, and apparently no other program on earth can see any changes it's made.  Gonna have to try something else!

Ummm are you saving the file as what ???? 
when in Paint.Net ?

Also, wanna make really sure, ( its happened to me) that somehow the file "NAME" didn't get changed somehow, or when you go to put it back in the Aircraft - it won't read and NOT show up ! 

Also what Aircraft are you painting ???? 

Jetranger.

I'm repainting the default King Air.  I'm saving as whatever the name will be, just like he does in the video, just clicking OK.

Oh... also, Paint.Net's "Lasso Select" tool SUCKS lol.

YAY!  Got GIMP to work with DXTBmp... you have to "export" rather than just hit save, so you can make it a .bmp instead of a .xcf, which apparently DXTBmp doesn't know what to do with.  Hopefully I'll get a screenshot up tomorrow!