Go to Hometime Projects, and click Ceramic Tile. You'll get more info than you care but it's very useful.
A couple of things I want to add ... If you install right over what you currently have, your floor will be about 1" higher than it is now. Check to see if this will cause any 'transition' problems with any doorways (with doors) or any doorways into other rooms. You may have to rip up what you have to make use of the rough construction.
If the room below the kitchen is not heated, the floor will be cold. There are warm floor systems to consider in this situation. Also, if you drop almost ANYTHING, it will either break, or chip the tile. And if the subfloor construction is 'marginal', you may have separation between your tiles from movement of the floor. If you have a concrete slab, to me, that's the best of all cases to install a tile floor. (It won't move AND it's conducive to installing a warm floor system.) My unsolicited $.02 is to say to go out and look at top-of-the-line vinyl flooring. There's some real nice stuff out there. They have wear-through material now so the prints don't 'rub off' like they use to. And the durability is very good. If you have kids growing up, you'll be glad you have vinyl.