not quite, norm.

hashing is more or less a relic (although relic is the wrong word) from cryptography. one example of a bad way of hashing would be to add up every byte of the file squared by the position of that bad. there are many different ways to hash a file, most clients today support an SHA1 hash, which is supposed to be unique per filesize. so, one file that's 500MB wouldn't have the same hash as another file that's 500MB unless they're exactly the same file. this is completely disregarding the file name.

the very nice thing with hashes is that people can change the filenames of files, but limewire (and other clients) will still be able to identify the specific file.