Just did this (see related msg. above for a problem you may eventually run into). It's not really a problem to take the radiators out. Drain your heating system--at least down to below the level of your bathroom floor. Usually there's a water outlet somewhere on your furnace. (P.S. Make sure you don't turn the furnace on when the water is out) Now you can unhook the radiator by unscrewing the big nuts connecting it to the pipes. Be ready with a towel or 2 since there will probably still be water in there that will spill out. Depending on ths size, you or you and a friend can haul the thing out of your bathroom so you can do your tiling.
The problems, if any, seem to come on reinstalling. By tiling, you have probably changed the level of the floor in the bathroom somewhat. Unless the water pipes that were connected to the radiator have a lot of vertical play in them, you may have to cut some new pipe to reach up to the level of the connection. This can be tricky if you're not a plumber, but not impossible. Once/if you get the floor tiled and radiator reconnected you have to fill your heating system with water (hopefully see answers to msg. above), bleed the radiators, and you should be good to go. Bottom line: Not terribly difficult, but definitely not a 5 minute operation, and may require a good chunk of extra work.