racear
Think you already have a SS and you know what you need regarding the Step/Dir to Analogue convertor so the other things you will need are probably some form of breakout board and some means of turning 5V into 24v and 24v to 5v. Well I am presuming your drive I/O will be 24V? Relays can do that easily abd fairly cheaply. A PLC can also do it over ModBUS but that will be more expensive.
As for software then really only Mach and Windows 2000, XP or in my opinion as a very last resort Vista, but I know some strange people actually like Vista

Hood