The cnc programs that drive stepper motors all talk directly to the parallel port. This is something Windows XP does not allow. Windows 95, 98 is ok.

You need the computer right beside the Cnc machine anyways, so why not find an old beater just for the cnc. I use an old pentium 166 for my cnc router and it works great. They can be had for free sometimes. I ran a network cable up to the garage so I do my designing in my office where it's comfortable, then send the file up to the garage where I cut my parts.

Eric