Hi,
A lot of it depends on how involved you want to be with the control software or do you want more of a turnkey system, I assume you have the physical machine, steppers and stepper drivers, a lot of users either use Mach3 ( MS Windows based ) or LinuxCNC linux based, both systems use a parallel port to interface to the stepper drivers, I have been using LinuxCNC now for a number of years without any real issues.
You could try LinuxCNC for free ( it is open source and very flexible - but you do need to put some effort in, take a look at LinuxCNC.org), There may also be evaluation versions of Mach3 available also, perhaps others can add more.