You can put ceramic or stone tiles directly over your painted brick provided that you rough up the gloss paint finish a bit with some sandpaper and you use a fortified thinset mortar (don't buy the pre-mixed kind) to adhere the tile to the brick. I suggest you buy a cheap tile saw (they have a $100 model at HD that looks like a small table saw that will do what you need for this). If you've never done tile before, you should read up on it a bit, but it's not that hard if you are patient.

I did the same thing in my house - I spent a little time getting about 50% of the paint off and the other 50% roughed up, as ventupete says. I'm sure I didn't need to remove any paint but went halfway due to conflicting advice on various Internet forums. Also, I built a new surround and mantle, sized so as not to have to cut any tiles. A friend did his using construction adhesive and it turned out surprisingly well. How he got the tile surface flat I don't know - must have begun with a very flat brick surface.

Getting the tile surface flat is relatively easy. The key is to trowel a layer of the thinset mortar over the brick surface which fills in the mortar joints and smooths out any irregularities in the brick surface.