I'm sure you could also make a CNC with the PowerPro256. You would just have to take extra steps to shield your PC, all wiring and circuit boards from the high frequency it produces when cutting. The reason I chose the PP50 was because it is non-high frequency start. I haven't had any problems with mine as of yet.
The process of cutting with a CNC is this. First you have to make the drawing of what you want cut. I use AutoCAD, but there other programs out there. Step 2 is bringing that drawing into CAM software where you import your part, set the material you are cutting, material size, where the part is nested in relation to the material, create the cut paths, feed rates, pierce height and cut height. I use SheetCam for this. SheetCam then creates the code that tells the CNC what to do.
I use Mach3 to run my CNC table. The first thing I do is zero my table. Mach3 has a button for this. The table will automatically move the table until it hits the installed home switches and stop. This is your table zero. Now that your table knows where it is at, it will not move out of predefined limit setting you set in Mach3 called soft limits. BUT if something still does go wrong, I still have limit switches at the corners. Now that your table knows where it's at and the gantry is squared up, you load the code into Mach3, tell it where the edge of the plate is and the top surface of the plate is (material 0,0,0), hit "run" and tadaa, the cutting begins.