try sun.java2D.opengl = true; to let openGL work and on windows, Graphics2D world work in DirectX way first try sun.java2d.d3d = true; to get faster maybe

U can use getAwtImage() to get a BufferedImage of a GreenfootImage creat a Graphics2D on that BufferedImage, and then do your painting on the Graphics2D could be better(I guess :) some set jobs on Graphics 2D could bring the paint jobs to GPU I would chet that out Later

if you want some some new effects you can look into my STG mode "ForceField" all explode effects are generated by codes without pictures and I want to know... why you let windows to kill the others...