Can I install ceramic tiles over ceramic tile flooring?

I don't think I would, if it is a shiny glazed tile in place now, There wont be a bond between the old and new tiles.

If the current tile is a rough slate tile, maybe.

Check the recommedations of the manufacturer of the tile you want to install.

Another option is to install 1/4 inch concrete backerboard over the existing tile, but it should be screwed down and that's a real chore in your situation.

Maybe the manufacturer knows of a type of mortar that will work on those smooth existing tiles (assuming they are smooth).

another answer:

my answer is no because it can be easily broke. this property is enought to answer absolutly no.

Another Answer: Don't do it. First, it will make your floor really high, this will be a problem especially if it butts up against another type of flooring such as carpet. Second, the bond of the mortar won't be as strong, you will end up needing to make repairs to the new floor much sooner than you would if you installed had it correctly the first time.

In response to installing cement board over the old tile... you can do this, it will get you a stable surface and a good bond for the mortar, but your floor will be really, really high. If there is a transition to another flooring type you will be stubbing your toes for years to come.

I would recommend doing the job right the first time around. Rip up the old tile, then install the new flooring. It will save you many headaches down the road.