Stumbled on these schematics. Beware the serial one will likely need some supply voltage adjustments to not destroy flash chips.
Both will also be very slow. But the basic idea in them is good.
Serial: http://www.mypicx.com/uploadimg/441880775_01272009_1.gif Parallel: http://www.mypicx.com/uploadimg/1652315010_01222009_1.gif
//Peter