It baffels me as to why people paint a 'surface' that was, well, maintenance-free. Maybe they're masochistic.
If you bought your home thinking you can restore the fireplace relatively easily, you're gonna be very disappointed. Depending on whether the paint is latex or oil-based will determine how to approach this job. There's some interesting info at Scrub-A-Home. They do brick restorations. One of their discussions is about having to 'wrap' a house in plastic to allow their chemicals to break-down the oil-based paint on the brick. (Can you imagine.) BUT, this is their livelyhood. The site is worth visiting. Maybe you can contact them for help. Ask: 1) How do I tell if the paint is latex or oil-based, and 2) What chemical AND manual-methods do you employ to do the job? Maybe you can buy some 'stuff' from them. Offer to do so as a courtesy for their free advice. Most chemicals in this type of work seem to be 'propietary' anyway so you may end up ordering something from them anyway.
In closing, here's another one of our estute Follow-upper's comments on this subject: That's Too Bad My best to ya and hope this helps.