Just an FYI about computers running Mach3.
I have discovered that the built in PP can cause symptoms that look as if the CPU is not fast enough when actually it is the PP chip, (sometimes built into the bridge).
My current computer misbehaves if I use the built in port, so I disabled it and use PP port one and two from an add-in PCI card. Works fine that way.
You can check this out easily by watching the task manager. If the CPU is not pegged, but the machine starts acting up, it may be the PP, which is semi-autonomous and can cause problems even if the CPU is humming along fine.
Also don;t assume that the drivers that come with an add-in card will work with Mach3. My card has the Mos chip and the drivers that come with the card do not work. The drivers from the Mos site, however, work fine.