If you decide to put vinyl over them you must glue a 3mm sheet of ply over the existing tiles first in as big a piece as you can, any joints in the ply must be filled and sanded flush. The reason for this is to prevent the shape of your old tiles showing through your new vinyl in about 3 to 4 weeks, also, it gives you a warmer floor to walk on. Make sure you degrease your old tiles first, the glue I would recommend is Gripfil, this comes in a tube and you apply it via a skeleton gun the same as used for silicon etc. (God help the person that has to get the ply up in years to come). To glue your tiles use tile to floorboard adhesive, (available from �Topps Tiles� if you have one near you). The only down side to this is that you might have to plane some timber off the bottom of any doors that open over the tiles. Good luck.