If you're going to cover the fireplace in wood I would recommend installing strips of wood running in the opposite direction of the finish wood. This will give you something to nail into. To secure the wood I would drill holes with a hammer drill, install lead inserts and then screw it to the brick. The addition of some construction adhesive would be a good idea as well. You can use shims to make the furring strips level if the brick is uneven.
Make sure that you check into the fire code and how it relates to the type of fireplace you have e.g., wood, gas. before installing wood.
I like the Idea of venetian plaster myself. I've used clay plaster before and gypsum plaster with the color mixed in. Here's a link to an album showing both of those fire places. Let me know if you want further info on plastering brick. Picasa Web Albums - jesse - Three fireplaces