Homebrew PCBs

Hi, I just discovered this group.  I am interested in using a plotter 
to directly lay down resist for pcb boards.  I picked up an HP 7475A 
plotter a few years ago and modified it to accept a pin according to 
plans I got from someone in Australia, I think.  The plotter appears 
to work OK. I say this based on the self test.  Also I hooked it up 
to my old PC and it printed at least one sheet OK.  But now I have a 
newer PC that runs XP.  It does have one serial port but I have not 
been able to get it to respond.  I have the owner's manuals for the 
plotter.  I also use a cheap windows-based CAD program called Key 
Cad.  I have been able to draw pcb layouts manually but would like to 
output to the plotter.

Any suggestions.

Thanks,

Jim, W7PUP