The attached Script-fu file is a modified version of B-Ranger's arrow drawing script. This version allows arrows to follow curved paths (splines) as well as maintaining the original scripts ability to draw straight arrows. (See http://registry.gimp.org/node/20269 for the original script)
To use the script:
1. create a single path of two points (the first point will be the one at which a single arrow head is drawn)
2. bend the path to the desired shape if a curved arrow is to be drawn
3. run the script by selecting "Arrow." from the "Tools" menu
4. adjust the settings as required and draw the arrow
I have found that with the default settings curved arrows look rather chunky - a setting of something like 5 for the brush size and 100 for the length of the wings looks better - but that's how I see it - play with the settings until you get what you want.