Im just using a five year old dell optiflex 32bit desktop computer with the on board graphics switched off in bios, and a pci graphics card installed.
Its running xp pro, and outputs to a uc300 .
What thats connected to has no bearing on Mach itself, it matters not if your connected to a machine the size of a house or a little Chinese bench top. as long as you have set it up mechanically and electronically correctly.
I personally always use servo's on my retrofits because they are worth the extra effort 100 times over, and essential when doing the kind of work I do where I cannot afford to miss steps.
Your best bet is to get a machine with brushed DC servos on it as this will simplify matters if you need to buy new drives.
My ATC, which is very rarely used, is one I designed myself using a swing in carousel , I modified the VB script available somewhere here to make it work, although im sure you could get something like a little "click" plc to handle that if you wanted
Hope that helps
Tony