Hi!
There are several ways to make files invisible in OS X. If the invisibility flag is set, you can make it visible using the command SetFile, which is part of the developer tools.
/Developer/Tools/SetFile -a V /path/to/fileorfolder
will make file invisible,
/Developer/Tools/SetFile -a v /path/to/fileorfolder
will make is visible again (notice the capital V in the first example).