Undecorated, alwaysOnTop, centered PROCESSING.ORG Frame (tested on 1.5.1)

gistfile1.java

boolean drawOnce;
int w = 640;
int h = 480;

void setup() {
  drawOnce = true;
  frame.removeNotify(); 
  frame.setUndecorated(true); 
  frame.setAlwaysOnTop(true); 
  frame.addNotify(); 
  size(640,480);
}

void draw() {
  if (drawOnce) {
    frame.setLocation((screen.width-w)/2,(screen.height-h)/2);
    drawOnce = false;
  }
  background(125);
  fill(0);
}