As the other answers here point out, anonymous ftp is usually stored under /home/ftp or /home/ftpd. However, I think that it is important to say that you do not want to hide the other folders. In the case of anonymous ftp, you do not want these users to have access to your entire filesystem for security reasons. To prevent this, ftp will move the root filesystem from / to /home/ftp. The other folders (like bin, lib, etc.) are there so that anonymous ftp users can have access to commands like cd, ls, get, etc. Moving or hiding these folders *may* break these commands, as well as some other functions.
Mark