[Endoperez]

I use MsPaint for the extraction because it's very quick to use and to open. Once I define the image size to 64x64 it's very easy to paste, copy unit, ctrl+n for new 64x64 blank, paste, edit and save. I could do the same in Gimp, but it opens much more slowly.

I use IrfanView to open Paint-saved .bmp files and to save them as targa files Dominions uses.

I use Gimp when I need to change the colors of the unit or of (some of) its equipment. It's easy to change e.g. all blue of a Ranger's (LA Ulm) clothes to green. The things you want to be able to do are:
1) use the color changing/shifting tools, and the blurring tools
2) use various selection tools (by area, all similar color, the magic wand selector tool) to restrict e.g. the blurring or the color shift into just parts of the sprite
3) use the basic tools for pixel-by-pixel editing to change one weapon to a different one, or to make a shield or change the shield's type, or to add a symbol, or to make an attack sprite.
4) use layers.


Examples:
You take a LA Ulm Ranger: a crossbowman clad in green. You choose a correct option from the toolbar and get to a window that lets you change all blue in the picture to a different hue, e.g. green. the boots are now discolored, so you paste another ranger into another layer, copy the original boots and paste them on the green one. Ta-da: a William Tell the Marksman!

You take a Vanir, and remove the horse. You take a Wyvern. You select the Wyvern's wing and move it into a separate layer. You add the riderless Vanir to a third layer. You realign the layers so that the rear wing is behind the Vanir, but the front wing is before him. Ta-da: a Wyvern Knight!