I'm in the same boat where I work with XP running on our CNC machines. You can only lock them down so much and still have support from the manufacturer. It's just a standard xp box like any office pc would be running. The machines are all on the office network and are connected to the internet. It is just too valuable to keep them off the network. The foreman who is operating the machine can look at shop drawings on the manager's computer. Someone in the office draws a piece of furniture in sketchup and can export a cut list directly the the CNC machine ready to run. Run a sheet of material on the machine and it deducts it from the materials inventory. etc etc etc