Homebrew PCBs

Hi, I have recently rescued a HP 7475A plotter and I am looking at 
converting it to handle pcb scratch etching (I think the mechanism is 
nowhere near strong for milling).
My question is do any members have any good links or files on scratch 
etching?
I am thinking either direct copper-scratching (styluses??) or 
scratching though an etch-resist and etching the board as normal.
Has anybody tried this? 
What type of results did they get on track resolution??

regards, PK