How do I hide folders in OSX?
The command-line way:
Open Terminal (/Applications/Utilities) and type
chflags hidden /path/to/folder
replacing /path/to/folder with the POSIX-style path to the folder you want to hide (for example, a folder on your desktop called test would be ~/Desktop/test).
To unhide it, type chflags nohidden /path/to/folder.
The freeware way:
I haven't used it, but I've seen the app Hide Folders, by Altomac.
Any file or folder that begins with a . will be hidden by default, although you can use a utility like TinkerTool to override this.