http://forum.thegamecreators.com/?m=forum_view&t=154983&b=3
That will point you to all your needs. Its a comiled list of nearly all the available software for creating media. With better way to descirbe it, you draw the textures as you would a picture or a painting. Its a little harder with a mouse so try getting a graphic tablet if your serious about this. Wacomm Bamboo are cheap enough and provide all the right functions youll need.
Thiers no easy way to descirbe since first hand experience is the easiest teacher. Download GIMP, Generic. Image. Manipulation. -something-
Then open the texture in the Gimp that you want to change. You can edit the colours, change designs pretty much do waht you want inside the textured area.
Heres at hand example of a UV map.
From this you can draw inside the areas and create your own textures for your model. Its quite a simple process if someone has already uvmapped. Just go nuts and play about on the ones you were given.
-Con