Learn how to make a muzzle Flare using Gimp and Sony Vegas Pro.
How to create a muzzle flare with Windows Movie Make or iMovie:
Do the same thing I did with gimp but instead of opening up your editing software, open up the frame you want the flare on with Gimp. Paste the flare you created earlier and shrink it and move it into position. Save it and edit you film as normal.