I used to have a home-converted Proxxon MF70 so might be able to help. What do you have with it and what do you not? As long as you have 3 working stepper motors you probably need a control board, a PC and a copy of Mach3 or LinuxCNC. There are various options on the board depending on whether you want to go for cheap or quality.

The MF70 is a nice mill if you're happy doing very small stuff. It doesn't have ball screws but is a bit small to need them to be honest.