FTP by itself is very insecure. Passwords are sent in plaintext over the internet; there is no encryption. You can set up FTP with an SSL certificate, but it can be complicated. This is where sFTP comes in. sFTP is FTP encryped with an SSH layer. freeFTPd is a free sFTP server. It's very easy to set up the server, set up users, view logs etc. Its a lot more secure than FTP. To give you an example of how much more secure it is, the strongest SSL certificate is 256 bits. With SSH you can go all the way up to 4096 bits!
freeFTPd is freeware and compatible with any Windows NT based system (eg. XP, Vista, 7, 2003, 2008). You can download it from http://www.freesshd.com/?ctt=overview