it looks like @LiveLoveDIY did that here: http://www.hometalk.com/1159330/diy-chalkboard-file-cabinet
If you have a small number of cabinets, use spray cans.......if you have a large number of them in an occupied space then call in an electrostatic spray professional: http://www.pnpcraftsmen.com/blog/electrostatic-painting-lockers-railings-storefronts-in-new-york
1) Scuff the surface with some sandpaper
2) Tape off anything you don't want painted
3) Prime with an oil-based spray paint.
4) Paint, use Rustoleum if you have any rusty spots otherwise, any kind of spray will work. Follow the instructions on the can. Do as many coats as you need for full coverage
5) Remove tape and Voila!