Agree 100% with George.!!

But if you must go with PP then I wouldn't buy a newer PC because it's highly likely it will be 3.3V and the CPU with have energy saving features you can't turn off which is what causes lot of the problems people have with PP.
You can buy Breakout boards that will buffer and boost signals to 5v but this is work around and not idle really.

PP is dieing donkey and unless your just testing the waters with CNC then I wouldn't waste a penny buying with PP in mind. A Motion control card is the only way to go really if you intend keeping with CNC and the extra initial cost will pay back long term in hassle free cutting. Also because most Motion control cards sits between PC and CNC control side they can move with you from machine to machine without too much hassle.