The Conquerer MPC5 card is indeed a serial card with its own onboard controller to interpret the conmmand stream from Eaziform's EasyCNC software. It will not be possible to use this with MACH3 (there are several threads on CNCZone about this). EasiCNC software is well thought of apparently, but it costs - you should download a trial from their site and see if it suits your needs. If you want to use MACH3 you will need to gut the MD5 and Ash cards and replace with new stepper drivers (and probably new steppers too)