From the MachSupport web site:
Mach4 Recommended Requirements:
PREFERRED: 32 or 64-bit Laptop or Desktop – Using an External Motion Controller
    Windows XP, Windows Vista, Windows 7, and Windows 8
    An appropriate external motion controller
    Mach4 Plugin for the selected Motion Controller
    2Ghz CPU
    1GB RAM
    Video Card with 256MB RAM(Large G-code files, especially 3D files will require a video card with 512MB RAM or higher)
*Use of Parallel Port for machine control only with desktop style computers with 32-bit versions of windows 7 and below.
32-bit Desktop – Parallel Port Recommended Requirements
    32-bit version of Windows XP, Windows Vista, or Windows 7
    Mach4 Parallel Port Legacy Plugin (cost applicable)
    2Ghz CPU
    1GB RAM
    Non-integrated Video Card with 256MB RAM(Large G-code files, especially 3D files will require a video card with 512MB RAM or higher)