What can I do to reduce the "Noise" on the parallel port test? I have time variation of 9-12us when using the pulse test engine. I am using a machine with XP Pro, Intel E4600 CPU, 1G ram. I have done the XP optimization but with no improvement.

The system will only be used for Mach3, no Internet or anything. Is there more I can do to try and improve the pulse engines consistency? The Mach3 config PDF doesnt actually say what to do if your system responds with spikes(unless I just can see it in the doc).

Have a look in the BIOS and see if there are any power saving options, I seem to remember Intel CPU based motherboards can have these options.
A PCI parallel port may help you but they can also have issues unless they are true parallel ports, most are but some are not.
Hood

If you have onboard graphics this can cause problems. Some have disabled the onboard graphics in BIOS when they have fitted a PCI type graphics card.

Tweakie.