I love tile fireplaces! I think it is the easiest and cheapest way to go. Many times cheaper than stone or paying a mason to brick it. Even assuming you have no cracks in existing, I would apply cement backer board so that all is regular and flat, etc.. The best way to do this is to remove the paint and to use thinset mortar to mount the backer and the tile. This will insure you won't get any cracks in the future. I had spectacular and inexpensive custom mantel results from: http://www.netease.net/amc and I saved a bunch by getting one that they posted on ebay.com for over $100 off regular price! They easily fit almost any fireplace. It is worth checking out their order form to see how it is possible to do things right on the web.