It's possible for files to have the same hash, yes - a "collision" in the hashing algorithm. The MD5 algorythm is designed to minimise this happening - the chances of two files producing the same hash are something like one in several billion. However, bear in mind that that's for the contents of whole files - hashing different data (i.e. strings representing file modification and size data) might cause more potential collisions. Wikipedia's MD5 page would probably be a good place to start reading up.
If it's just name/size etc, isn't it possible for files to have the same hash but be totally different?