I found out about the tutorials at the GIMP website ([The GIMP](http://www.gimp.org)), so I tried out some of them. The most impressing tutorial for me has been the [“Draw A Paint Brush”](http://www.gimp.org/tutorials/Draw_A_Paint_Brush/) tutorial by Tuomas Kuosmanen. You can see the resulting image at the left, I’m going to put the gimp source file up when I’ve got more time.
This is the Paint Brush in its original size, hope you like it!
My girlfriend told me she wanted to have a colour palette for the paint brush, so I tried it out. It’s not that good, but it’s a start :).
This is a merged image of the Colour Palette and the Paint Brush.
René's Blog 
Thanks for this valuable post. I love gimp.