Let me add, you can also do something much simpler, which is create a larger "layer" of all white for your glow around your bullets, and then do blendmode on it
Like this (see the player with glowing armor, and glowing bullets):
Here's a link describing creating the glow image.
See my blog entry here detailing the code to do this. You can find gimp tutorials on how to create the fuzzy white outlines for the glow effects.