Thank you all for your input. Everyone who replied had something different/additional to tell me. For this I am grateful.
I already have an Eckler rt stepper dongle to supposedly use a USB connection to the controller. Like all too many objects being sold via the Internet, it arrived without software or any instructions for use. Even I know that without a driver, no USB device is likely to work unless it is registered with Microsoft and Windows automatically knows what it is. That isn't the case with this device. Looks like I've done $85 on this one so any suggestion I use one I'm sceptical about.
I looked (briefly) at WinCNC and left the site after reading the first line of its description. "WinCNC is software and hardware package that allows control of a CNC machine" at $1200 for a daughterboard and few bucks worth of accessories, I can't see any real value in it except the likelyhood of more PayPal intervention for a refund when it doesn't drive my router.
Linux CNC is a neat looking interface. It has support for G540 controller but not the 'nowandforever' VFD. I guess it wouldn't be too hard to go back to using the controlls on the 'black box' to adjust the spindle speed but it is much nicer to let the Vcarve Gcodes do it for me.
I guess in reality, Mach3 looks like to only viable alternative. I found information on running it under Windows 7 and some sketchy details about getting it to run under Windows 8. It seems the developers could have done this themselves but chose instead to support Mach4 and charge users who have a parallel port configuration for making it backwards compatible.
I'm afraid I don't subscribe to the therory of making millions of dollars selling a few lines of code. I don't have a problem paying for the work that goes into developing a complex program like Mach but at some point stopping support for a program still being sold doesn't do a lot for the developer's ethics. BTW. Its illegal to do that in Australia but not being in a country with strong consumer laws makes it easy to abandon any ethics that produce respected companies in the search for undeserving profit.
Again, Thanks everyone for sound advice. Looks like Mach3 is my only viable choice. USBCNC software needs a Planet CNC controller board if you plan on updating it or forever you'll be annoyed by a nag screen telling you to update its firmware. A real pity because it is both easy to use and easy to configure.